stem cells and cancer stem-like cells in endocrine tissues

Stem Cells and Cancer Stem-Like Cells in Endocrine Tissues

Ricardo V. Lloyd & Heather Hardin &

Celina Montemayor-Garcia & Fabio Rotondo &

Luis V Syro & Eva Horvath & Kalman Kovacs

Published online: 23 February 2013# Springer Science+Business Media New York 2013

Abstract Cancer stem-like cells are a subpopulation of self-renewing cells that are more resistant to chemotherapy andradiation therapy than the other surrounding cancer cells. Thecancer stem cell model predicts that only a subset of cancercells possess the ability to self-renew and produce progenitorcells that can reconstitute and sustain tumor growth. Evidencesupporting the existence of cancer stem-like cells in the thy-roid, pituitary, and in other endocrine tissues is rapidly accu-mulating. These cells have been studied using specificbiomarkers including: CD133, CD44, Nestin, Nanog, andaldehyde dehydrogenase enzyme. Putative cancer stem-likecells can be studied in vitro using serum-free mediasupplemented with basic fibroblast growth factor and epider-mal growth factor grown in low attachment plates or inextracellular matrix leading to sphere formation in vitro. Can-cer stem-like cells can also be separated by fluorescent cellsorting and used for in vitro or in vivo studies. Injection ofenriched populations of cancer stem-like cells (also referred toas tumor initiating cells) into immunodeficient mice results ingrowth of xenografts which express cancer stem-like bio-markers. Human cancer stem-like cells have been identifiedin thyroid cancer cell lines, in primary thyroid cancers, innormal pituitary, and in pituitary tumors. Other recent studiessuggest the existence of stem cells and cancer stem-like cellsin endocrine tumors of the gastrointestinal tract, pancreas,lungs, adrenal, parathyroid, and skin. New discoveries in thisfield may lead to more effective therapies for highly aggres-sive and lethal endocrine cancers.

Keywords Cancer stem-like cells . Thyroid . Pituitary .

Carcinoid . Adrenal cortex . Parathyroid

Introduction

Endocrine tumors are relatively uncommon. Thyroid canceris the most common endocrine malignancy and comprisesabout 1 % of all malignancies in the USA [1, 2] and pituitarytumors constitute about 10 % of intracranial neoplasms [1].Studies of stem cells and cancer stem-like cells (CSCs) arerelatively recent, although the existence of stem cells hadbeen postulated for some time [3].

There are two major types of stem cells which includeembryonic stem cells and adult or somatic cells. Embryonicstem cells can generate all three germ layers and all differen-tiated cells while somatic stem cells have a more restrictedability to differentiate. Embryonic stem cells are totipotentcells up to the eight-cell stage of the morula. Cells of the outertrophoblast layer surrounding a core of cells from the inner cellmass. Although these cells are no longer totipotent, they candevelop into variable cell types of the embryo. The first humanembryonic stem cells derived from human blastocysts werereported in 1998 [4]. Embryonic stem cells have a great deal ofplasticity and are able to self-renew. Among the adult stemcells are CSCs which are also known as tumor-initiating cells.The CSC hypothesis is becoming widely accepted, althoughthere is still some skepticism about the existence of CSCs [5].

Thyroid

Thyroid stem/progenitor cell-like characteristics were studiedin the mouse thyroid by Hoshi et al. [6]. These investigatorsisolated side population cells which were characterized bytheir ability to efflux the vital dye Hoeschst 33342. This sidepopulation was defined as a subpopulation of cells within the

R. V. Lloyd (*) :H. Hardin : C. Montemayor-GarciaDepartment of Pathology and Laboratory Medicine, University ofWisconsin School of Medicine and Public Health,K4/436 CSC 8550,Madison, WI 53705, USAe-mail: [email protected]

F. Rotondo : L. V. Syro : E. Horvath :K. KovacsDivision of Pathology, St. Michael’s Hospital, University ofToronto, Ontario, CA, USA

Endocr Pathol (2013) 24:1–10DOI 10.1007/s12022-013-9235-1

sample which had the ability to rapidly efflux Hoeschst 33342dye and represented a stem-like cell population in the mousethyroid. Stem cells/progenitor cells have the ability to excludethis DNA binding dye because of the presence of breastcancer-resistant protein-1(ABCG2), an ATP-binding cassettetransporter that is associated with multidrug resistance inmany cancers by pumping out the drug. These cells werehighly enriched for stem/progenitor activity [6]. The sidepopulation cells expressed octamer-binding transcription fac-tor 4 (Oct4) and nucleostemin, while the genes for thyroiddifferentiation markers, such as thyroglobulin, thyroid perox-idase, thyroid stimulating hormone receptor, and thyroid tran-scription factor were expressed at very low levels. Hoshi et al.performed three-dimensional primary cultures and the cellsformed epithelial arrangements and follicle-like structures thatexpressed thyroid transcription factor1 and thyroglobulin. In amore recent study, Ozaki et al. [7] performed partial thyroid-ectomy in mice and observed that they were cells with follic-ular and C cell features which were altered to becomeimmature cells. The authors suggested that the immature cellsmight be derived from stem/progenitor cells on their way todifferentiation into C cells or follicular cells. They postulatedthat these cells may participate in the repair and/or regenera-tion of the thyroid gland [7].

Several reviews have summarized recent findings aboutthyroid stem cells and thyroid CSC [8–14]. Adult stem cellshave been characterized in the thyroid gland by several in-vestigators [15, 16]. These cells have been shown to expressstem cell markers, such as Oct4, an embryonic stem cell gene,in tissues derived from adult human goiters. Clinically derivedhuman Oct4- and Nanog-positive (embryonic stem cell tran-scription factor linked to pluripotency) cells from thyroid goi-ters were reported to generate spheres in the presence of basicfibroblast growth factor (bFGF) and epidermal growth factor(EGF) which promote the maintenance of adult stem cells invitro, and in the absence of serum and thyroid-stimulatinghormone [15]. These cells could differentiate into fat cells afterappropriate stimulation but did not produce tumors in severecombined immunodeficient (SCID) mice [12].

Cellular Origin of Thyroid Stem Cells

The bonemarrow contains stem cells that are usually found in aspecific niche or microenvironment [16–18]. However theniche of adult thyroid stem cells has not been identified. Solidcell nests, derived from the ultimobranchial bodies, have beenreported to have stem cell/progenitor cell properties with thecapacity for self-renewal and an ability to differentiate intomore than one cell type [19]. These cells express p63 whichis thought to be a marker for stem/progenitor cells, and theygenerally do not express thyroglobulin or calcitonin. Recentstudies by Asioli et al. confirmed the expression of p63 bythese cells with weak staining for TTF-1 and negative staining

for thyroglobulin and calcitonin [20]. Classical stem cellmarkers, such as Sox2 and Oct4 have not been examined insolid cell nests, so much work needs to be done to characterizethe niche or microenvironment of adult thyroid stem/progenitorcells.

The cellular origin of thyroid cancer remains controversial.The classical concept is that anaplastic thyroid carcinoma arisesby dedifferentiation from well differentiated thyroid carcino-mas such a papillary and follicular carcinomas [21–23]. Evi-dence for this concept include the presence of areas of welldifferentiated carcinomas in the same cancers with anaplasticcarcinomas and the expression of BRAFmutations in 40–50%of papillary thyroid carcinoma and in a smaller but significantpercentage of anaplastic thyroid carcinomas.

It has been proposed that undifferentiated or anaplasticcarcinoma may originate from remnants of fetal thyroid cellsby Takano [24, 25]. Takano also proposed that papillary andfollicular carcinomas are derived from other fetal or devel-opmental cells. The fetal cell carcinogenesis hypothesis isclosely linked to the concept of thyroid CSCs and serves asa useful model for future experimental studies (Fig. 1).

Characterization and Properties of Thyroid CancerStem-Like Cells

Different approaches have been used to isolate and examinethyroid CSCs. Most have included in vitro labeling of theCSCs with specific biomarkers and subsequent enrichmentof the CSC population. A few studies have used frozen orparaffin sections to study expression of CSC biomarkers.Some studies have labeled cells with CD133 ( prominin-1)which is a transmembrane domain glycoprotein present onhematopoietic stem and progenitor cells from fetal and adultcord blood, peripheral blood, bone marrow and solid tissuesincluding glial, prostate, liver, and kidney [26–31]. Aldehydedehydrogenase (ALDH) and the ALDEFLUOR assay rely onthe presence of ALDH enzymes in normal and malignantcells. Some tumors such as mammary tumors have ALDH1activity associated with stem/progenitor cell properties [32,33]. The ALDEFLUOR-positive and ALDEFLUOR-negativecells can be separated by fluorescent activated cell sorting. Aspreviously mentioned, another method of detectingstem/progenitor cells involves the use of the DNA bindingdye Hoechst 33342 [33, 34], although this method is associ-ated with more cell toxicity (Table 1).

Other approaches to characterize CSC include culturingcells in ultra-low attachment plates, or with extracellular ma-trix in the presence of bFGF and EGF in the absence of serum(which can cause differentiation of CSCs) [33, 34]. CSCsform spheres which proliferate under these conditions [33, 34]

To confirm the presence of CSCs in an enriched popula-tion of separated cells, growth of the cells in immunodefi-cient mice is usually done. Investigators have used nude

2 Endocr Pathol (2013) 24:1–10

mice, SCID mice or more highly immunodeficient micesuch as nonobese diabetic/severe combined immunodefi-cient (NOD/SCID)/interleukin (IL)-2R8 null (NOG) micefor these types of experiments [32].

Specific biomarkers have been used to characterize CSCs,such as the CD44+/CD24− phenotype [35]. Other biomarkersthat are highly expressed in CSCs include Sox2, Oct4, andNanog, which are pluripotency genes activated in stem cells.Stem cells are also characterized by self-renewal pathways,such as Wnt/Beta-catenin, Hedgehog, and Notch [36–41].

Human Thyroid CSC Studies with Cell Lines

Mitsutake et al. [42] used Hoechst 33342 dye to identify CSCin various cell lines including FRO, NPA, TPC1, WRO, andARO. Two of these cell lines were subsequently shownnot to be of thyroid origin (ARO and NPA) by genomic

fingerprinting [43]. They found very small percentages ofCSCs in the cell lines (FRO, 0.1 %; WRO, 0.02 %; andTPC1, 0.0 %). They reported that the side population (SP)cells survived at a lower cell density. Gene expression profil-ing from SP and non-SP cells showed several genes associatedwith stem cell features that were upregulated (ABCG2 MYCand HES1). However, the non-SP population also containedcells that were tumorigenic in nude mice. The clonogenicability of the SP cells was higher than the non-SP cells.

ARO and FRO cells were studied for stem cell propertiesby Zito et al. after labeling with CD133 [43]. They did notfind any CD133-positive FRO cells, unlike the ARO cells[44]. In contrast, Friedman et al. [45] found CD133-positiveARO and FRO cells with about 7 % of each cell type labeledfor CD133. Most of the subsequent studies by Friedman etal. were done with the ARO cells which do not represent athyroid cell line [44].

Fig. 1 Diagramatic illustration of thyroid CSCs and their response toconventional therapy. These cells are derived from adult stem cells, butthe exact cell of origin is unknown as indicated by the question marks.They may come from stem cells, from progenitor cells, or from transientamplifying cells.With the development of a cancer, the CSCs are resistantto chemotherapy and radiation therapy compared with the other cancer

cells, so the use of conventional chemotherapy and radiation therapy donot destroy the CSCs and the patient undergoes relapse. Development ofspecific therapies to target and eliminate the CSC should lead to moreeffective treatment of high-grade endocrine cancers, such as anaplasticthyroid carcinoma by eradicating the thyroid CSCs followed by conven-tional chemotherapy and/or radiotherapy

Table 1 Methods used to isolateand characterize cancer stem-like cells

Flow cytometric cell sorting with ALDEFLUOUR, CD133, or Hoechst dye 33342

Cell culture in ultra-low attachment, serum-free conditions in the presence of bFGF and EGF

In vitro cytotoxicity assay to evaluate resistance to chemotherapeutic agents

Xenotransplantation into immunodeficient mice, such as nude and SCID mice

Endocr Pathol (2013) 24:1–10 3

Klonish et al. [7] examined the anaplastic cell line 8505Cwith ALDH1. They found 17–38 % ALDH1-positive cellsin this cell line. The ALDH positivity was inhibited in thepresence of diethyl-aminobenzaldehyde, which suggests thepresence of CSCs in this cell line [7]. Xenograft studies orsphere-forming assays were not done in this report [7].

Chen et al. [46] examined the antimitogenic effects ofmetformin, a drug that exerts a growth-inhibitory effect byreducing hyperinsulinemia. A doxorubicin-resistant thyroidcarcinoma cell line and thyroid cancer stem cells lines,HTh74 and HTh74R dox, were analyzed by clonal forma-tion assay. They found that metformin diminished growthstimulation by insulin [46]. The doxorubicin-resistantthyroid carcinoma cell line HTh74Rdox overexpressedthe stem cell markers Oct4 and ABCG2 which exportdoxorubicin out of the cells and confers doxorubicinresistance to these carcinoma cells, which is a commoncharacteristic of CSCs [46].

Medullary thyroid carcinomas (MTC) are thyroid cancersderived from neuroendocrine C cells which produce calci-tonin and calcitonin gene-related peptide. Most cases ofMTC are sporadic while a significant subset is inherited asmultiple endocrine neoplasia or familial MTC. Zhu et al.examined CSC in the MTC cell lines M2-CRC-1 and TT byimmunostaining for CD133 and flow cytometry analysis.The CD133-positive M2-CRC-1 and TT cells formedspheres in media supplemented with B27 (a commerciallyavailable stem cell growth media cocktail), bFGF, and EGF.The CSCs exhibited features of self renewal and multiplelineage differentiation that was dependent on ret proto-oncogene receptor activity [47].

Human Thyroid CSC Studies with Primary Tumors

Todaro et al. [36] analyzed primary resected thyroid carci-nomas including papillary thyroid carcinoma (18 cases),follicular carcinomas (10 cases), and anaplastic carcinomas(6 cases) using ALDEFLUOR cell sorting. They performedclonogenic assays starting with one cell per well and ana-lyzed the spheres after xenograft injections in nude mice andin NOD/SCID mice. They found more sphere-forming cellsin the anaplastic carcinomas compared with the papillaryand follicular carcinomas. The anaplastic carcinomas had10-fold higher levels of ALDH1 mRNA compared withpapillary and follicular carcinomas. All of the thyroid cancerspheres were highly tumorigenic with as few as 5×103 cellsinjected. Orthotopic injection of 100 cells from tumorspheres led to enrichment of the ALDH1-positive cells inlung metastases compared with the thyroid tumors.Malguanera et al. [48] used three primary papillary thyroidcarcinomas to establish thyrospheres using serum-free andultra-low attachment conditions. The spheres expressedstem cell markers including Oct4, SOX2, Nanog, CD133,

and CD44 and had low/absent thyroid-specific markersincluding thyroid peroxidase, thyroglobulin, and thyroid-stimulating hormone receptor. A novel finding was that bothinsulin receptor isoforms, IGF-IR, IGF-1, and IGF-TI wereexpressed at high levels in thyroid spheres and markedlydecreased in differentiating cells [48].

There are only a few studies of CSCs biomarker expres-sion using formalin-fixed paraffin embedded thyroid tissues.Friedman et al. [45] used paraffin-embedded tissue sectionsfrom surgical pathology samples to show that CD133 washighly expressed in anaplastic thyroid carcinomas but not innormal thyroid cells. In a recent study of paraffin-embeddedtissues, Liu and Brown [49] analyzed two cases of thyroidcarcinomas and found CD133, CD44, and nestin, a neuralprogenitor marker, but no E-cadherin in both anaplasticthyroid carcinomas [49]. The papillary and follicular thyroidcarcinomas present in the adjacent areas of the two anaplas-tic carcinoma cases had lower expression of CD133 andCD44 [49].

Epithelial–Mesenchymal Transition and the Associationwith Stemness in Thyroid Carcinomas

Epithelial–mesenchymal transition (EMT) is a major mech-anism in tumor progression, local invasion, metastasis, andtherapeutic resistance and is linked to the development ofstem-like properties by cancer cells [50–52]. EMT is asso-ciated with loss of E-cadherin expression by genes thatrepress E-cadherin including zinc fingers Snail, Slug,ZEB1 and ZEB2, and the basic helix–loop–helix transcrip-tion factor Twist1. During this process, the cells lose cellularadhesion and polarity and acquire an invasive phenotype. Astudy by Vasko et al. in thyroid tumors showed that papil-lary thyroid carcinomas were characterized by EMT withoverexpression of vimentin which was associated with in-vasion and lymph node metastases [53]. EMT has also beenobserved in anaplastic thyroid carcinomas [54, 55] withdecreased expression in E-cadherin and beta-catenin com-pared with the differentiated thyroid carcinomas. One studyshowed upregulation of Twist1 in anaplastic thyroid carci-noma cell lines [54]. An earlier study by Hardy et al. [55]found expression of Snail and Slug in most (87 %) papillarythyroid carcinomas and in half of the follicular carcinomas.However, a recent study using tissue microarray with over130 thyroid tumors showed that only anaplastic thyroidcarcinomas expressed Slug and Twist1 while papillary andfollicular carcinomas as well as follicular adenomas andnormal thyroid were uniformly positive for E-cadherin[56] supporting the role of EMT in the development ofanaplastic thyroid carcinoma.

The induction of EMT and the expression of stem cellmarkers have been linked by experimental studies. Mani etal. [51] used a human mammary epithelial cell model to


show that acquisition of mesenchymal traits was linked tothe expression of stem-cell markers [51]. They also showedthat transformed human mammary epithelial cells that haveundergone EMT formed spheres, soft agar colonies, andtumors more efficiently [51]. The implication of these ob-servations is that the EMT program that enables cancer cellsto spread from a primary tumor may also promote their self-renewal capacity.

In addition to EMT, the reverse process or mesenchymalepithelial transition (MET) also has a central role in embryo-genesis and tumor progression. One group of investigators hasproposed that the expression of stem cell markers may reflecttransition of CSC states rather than generation of CSC fromnon-CSC populations [57]. Liu et al. proposed thatmicroRNAs, which are 18–22 nucleotide noncoding RNAsthat function as oncogene and tumor suppressor genes byregulating miRNAs, may regulate the EMT and MET transi-tion states [57]. Breast carcinomas in patients with bonemicrometatasis had cancer cells expressing CSC markers aswell as EMT markers [58]. These micrometastases are mostlyquiescent and did not express much Ki67, a marker of prolif-eration [59]. To enter a proliferation state, CSCs may undergoa MET transition and lose their invasive characteristics andacquire self-renewal capacity. These cell-renewing propertiesof CSCs could drive tumor growth at metastatic sites. In thismodel, the balance of EMT/METstates of CSCs are regulatedby microRNAs and play an important role in mediatingtumor invasion and metastasis as well as maintainingtumor dormancy or promoting tumor growth at themetastatic sites [57]. Such studies should be performedin thyroid cancers in the near future.

Pituitary

Embryonic stem cells can be induced to differentiate alongseveral cell lines. Recent studies have taken advantage ofthese properties to make advances in regenerative medicinefor the replacement of specific normal functioning pituitarycell types [60, 61]. A recent study by Suga et al. showed thefeasibility of developing stem-cell culture for generation ofanterior pituitary cells [60, 61]. They reported the efficientself-formation of three dimensional anterior pituitary tissuesin an aggregate culture of mouse embryonic stem cellstreated with reagents within the hedgehog signaling path-way. They were able to produce corticotrophs that secretedadrenocorticotropin hormone. When these cells were graftedin vivo they could restore normal corticotroph function inhypopituitary mice [60].

Most studies in adult stem cells in the anterior pituitaryhave been done in rodents and other vertebrates. Krylyshkinaet al. detected the stem cell marker nestin, an intermediatefilament protein that is mostly expressed in neuronal cells, in

the rat anterior pituitary gland. It was thought that the nestin-positive cells in cultured pituitaries had a mesenchymal phe-notype and that these nestin-positive cells were heterogeneouswith mesenchymal and putative stem/progenitor cells. In asubsequent study, Chen et al. used flow cytometry to identifyside populations in the pituitary of the mouse, rat, and chickenwith Hoechst 33342 dye [62]. This side population wasenriched in cells positive for stem-cell-associated factors in-cluding Oct4, C133, Nanog, Nestin, and stem cell antigen. Inaddition, signaling pathways commonly found instem/progenitor cells, such as Notch, Wnt, and Sonic Hedge-hog which are highly conserved were also present [62]. Theside population could also expand clonally into nonadherentspheres in vitro.

The study of Chen et al. [62] also detected SOX2, abiomarker associated with stem cells in the sphere-formingpituitary cells in culture. SOX2 was not associated with Pit1,the POU homeodomain transcription factor in the anteriorpituitary. However, SOX2 was frequently associated withS100 protein, a general marker of folliculo-stellate cells inthe anterior pituitary [62]. Several researchers have investi-gated the role of folliculo-stellate cells as potential stemcells which will be discussed in the next section [63–73]

Cellular Origin of Pituitary Stem Cells

The marginal layer adjacent to Rathke’s cleft is consideredto be the presumptive stem/progenitor cell niche in thepituitary. Folliculo-stellate cells have been studied by manyinvestigators and some have proposed that these may beadult stem cells in the anterior pituitary [62, 63, 67–73].Horvath and Kovacs reported that in a large series of pitu-itary adenomas and non-tumoral human pituitaries, the S100protein and glial fibrillary acidic acid immunoreactivity wasmost intense in newly formed follicles while the olderfollicles were negative. They proposed that endocrine cellsdedifferentiate into folliculo-stellate cells and represent atype of pluripotent adult stem cells. The studies of Inoue[73] also suggested that folliculo-stellate cells could bepluripotent since skeletal muscle could develop from pitui-tary cells when transplanted under the kidney capsule.DeAlmeida et al. also found that the pituitary folliculo-stellate cell line that they established, Tpit/F1, could alsodifferentiate into skeletal muscle cells [72].

Krylyshkina et al. [74] also found that nestin was presentin a small number of S100-positive cells. Jin et al. preparedenriched populations of S100-positive folliculo-stellate cellsafter immunohistochemical staining for S100 protein com-bined with laser capture microdissection. They found thatthese cells expressed transforming growth factor beta 1 andpituitary adenylate cyclase-activating polypeptide (PACAP)and PACAP receptors but not pituitary hormones indicatingthat there were not hormone-producing cells [75].


Folliculo-stellate cells may also become neoplastic, so ifthey are stem cells, they may be the neoplastic counterpart ofCSCs. Horvath et al. reported on two sellar neoplasms inwomen with ultrastructural features of folliculo-stellate cellswith networks of typical follicles and similarities to fetalhuman pituitaries at ages 6 and 10–12 weeks of gestation[68]. Vankelecom proposed that subsets of heterogeneousfolliculo-stellate cell population represented different stagesin the EMT process in the adult stem/progenitor cells [62, 63].

The studies of Gleiberman et al. using genetic approachesto identify adult pituitary stem cells have provided newevidence for the origin and differentiation of pituitary stemcells [76]. These authors examined nestin-expressing adultstem cells in the pituitary region of the mature mouseanterior pituitary to show that these cells could generatesubsets of all six terminally differentiated anterior pituitarycell types. They noted that these adult stem cells did not playa significant role in organogenesis, but did undergo postna-tal expansion and produced progenies consisting of differ-entiated adult type anterior pituitary cells [76].

Farquier et al. reported on a SOX2-positive cell popula-tion around the lumen in the marginal zone between theanterior and intermediate lobe of mouse pituitaries [70]. TheSOX2-positive cells were initially present throughoutRathke’s pouch and then became restricted to the marginalzone. In adult mice, SOX2-positive cells represented 3–5 %of the whole population of anterior lobe cells which wouldbe in the range expected for pituitary stem cells.

Cancer Stem-Like Cells in Pituitary Tumors

Most pituitary tumors are benign adenomas with a smallerpercentage of aggressive or atypical adenomas [1]. Pituitarycarcinomas with proven metastases contribute less than 1 %of pituitary tumors [1].

There are only a limited number of studies of CSCs inpituitary tumors [76–78]. Using the mouse model of nestin-green fluorescent protein (GFP) transgene, Gliebermann et al.[76] used mice with one functional allele of retinoblastomaRb-1 gene which invariably develop tumors in the intermedi-ate lobe of the pituitary during the second year of life. Thesemice were crossed with nestin-GFP mice and the offspringdeveloped intermediate lobe tumors at 12 months of age withmultiple nodules of proliferating endocrine cells predominant-ly producing melanocyte stimulating hormones. These nod-ules were composed of nestin GFP-positive cells thatexpressed stem cell markers including: SOX2, EpCAM, andcytokeratin 8 while the majority of the tumor cells weremelanocyte-stimulating hormone negative. The authorssuggested that these cells could represent CSCs [76].

Side population cells were recently reported in humanpituitary adenomas and ranged from 1.5 to 8 % of the tumorcells. The human adenoma cells were not analyzed for

additional stem cell features by Vankelecom and Gremeaux[64]. Yunoue et al. [77] analyzed a series of human pituitaryadenomas for CD133 expression and reported that 25.7 % ofthe 70 pituitary tumors expressed CD133 which was higher innonfunctioning than functioning pituitary tumors. There wasno correlation of tumor size or postoperative recurrence ratewith CD133-positive cells. The authors suggested that theexpression of CD133-positive cells in pituitary tumors wasrelated to immature endothelial progenitor cells that may playa role in the neovascularization of pituitary tumors [78]. Flowcytometric analysis showed that CD34 was coexpressed in28.8–96.0 % of CD133-positive cells. However, the CD133-positive pituitary adenoma cells also coexpressed nestin. TheCD133-positive cells did not express S100 protein or glialfibrillary acidic protein suggesting that they were not relatedto folliculo-stellate cells.

In a more extensive study of CSCs, Xu et al. coined theterm pituitary adenoma stem-like cells or, PASCs, to describecells with features similar to CSCs in human pituitary tumors[78]. These were able to grow tumor sphere cultures fromhormone-positive and hormone-negative pituitary adenomas.They used self-renewal assays, stem cell-associated markerexpression analysis of Oct4, NOTCH4, JAG2, and CD90 intheir analyses. The PASCs were more resistant to chemother-apeutic agents than their differentiated daughter cells and theyshowed that the PASCs were pituitary tumor-initiating cells inNOD/SCID mice using serial orthotopic xenografts. Thesefindings show that benign pituitary tumors may have CSCfeatures as has been reported for malignant neoplasm. CSCshave not been studied in pituitary carcinomas or atypicalpituitary adenomas as yet, but future studies with more ag-gressive pituitary tumors should provide new insights into therole of CSCs in pituitary tumors.

Gastrointestinal and Pancreatic NeuroendocrineTumors

Chemoresistance in many malignancies have been attributedto the presence of CSCs. Metastatic gastrointestinal neuroen-docrine tumors to the liver and other sites are oftenchemoresistant, but few studies have examined CSCs in neu-roendocrine tumors [79]. Gaur et al. analyzed primary gastro-intestinal neuroendocrine tumors and the cell line CNDT2.5for CSCs to uncover novel therapeutic targets for these can-cers. They used the ALDEFLUOR assay which had beenpreviously used in studies of primary thyroid and other cancers[33]. They examined 14 midgut carcinoids and five pancreaticneuroendocrine tumors to isolate single cells. ALDH-positivecell populations ranged from 0.5 to 20.1 % in carcinoids andfrom 0.2 to 5.9 % in pancreatic neuroendocrine tumors. TheCNDT2.5 neuroendocrine cell line had ALDH-positive cellsranging from 1 to 3 %. Sphere formation was not detected in


samples from ALDH-positive primary tumors. The ALDH-positive cells from the CNDT2.5 line produced tumors in 9 of20 mice, but tumors were not seen in the ALDH-negative orthe sham-sorted cells. The CNDT2.5 cells were capable ofanchorage-independent growth in ultra-low-attachment condi-tions. There was a markedly higher expression of Srcprotooncogene that regulates proliferation differentiation andapoptosis expression in ALDH-positive cells from theCND2.5 cell line compared with the ALDH-negative cells.These findings suggest that Src inhibition can decrease thepercentage of viable ALDH-positive cells. The authors con-cluded that carcinoid tumors have an inherent CSC populationthat may mediate resistance to systemic therapies. More stud-ies are needed with carcinoid tumors and pancreatic neuroen-docrine tumors to validate these preliminary observations.

Cancer Stem-Like Cells in Other Endocrine Tissues

Lungs

A few studies of CSC in pulmonary neuroendocrine tumorshave been reported [80, 81]. Jiang et al. [80] examined theachaete-scute complex homologue 1 (ASCL1) as a tumorinhibitor in human small cell lung cancer. ASCL1 is importantfor the development of normal lung endocrine cells as well asother endocrine and neural tissues. Microarray analyses iden-tified two candidate stem cell marker genes in small cell lungcarcinoma that were directly regulated by ASCL1 includingCD133 and ALDH1A. Xenografted tumors had high levels ofCD133 expression. The authors concluded that many cells inthe small cell carcinoma population had tumorigenic capacity.In a recent study of SOX2 expression in pulmonary neuroen-docrine carcinomas as well as other lung carcinomas, Sholl etal. reported that 91 % of small cell carcinomas expressed thisstem cell biomarker, while only 23 % of low-grade and 72 %of high-grade neuroendocrine carcinomas expressed SOX2.They also observed that SOX2 was highly expressed in con-cert with p63 supporting the observation that SOX2 wasassociated with a “stemness” phenotype that predicted poorpatient outcome [81].

Adrenal Cortex

Genetic analyses have found various signaling pathways inadrenal cortical cells including sonic hedgehog and Wnt.Sonic hedgehog was restricted to adrenal cortical cells thatdid not express steroidogenic genes, but gave rise to theunderlying differentiated adrenocortical cells [82]. Wnt/Beta-catenin signaling is thought to maintain the undifferentiatedstage of adrenocortical stem/progenitor cells through induc-tion of the target genes Dax1 and inhibin-alpha. These authorssuggested that adrenal cortical adenomas and carcinomas have

frequent constitutive activation of Wnt signaling due to loss-of-function mutations in the APC tumor suppressor gene orgain of function mutations in Beta catenin, hence the Wntpathways may be important in the oncogenic process ofadrenocortical tumors [82].

In an earlier study using the adrenocortical NCI h295Rtumor cells line, Lichtenauer et al. used Hoechst 33312 toisolate side population cells, but did not see differences inthe proliferative activity of side population and non-sidepopulation cells, and there was no survival benefits aftertreatment of cells with cytotoxic agents used commonly inadrenocortical carcinomas [83]. This observation raisesquestions about the existence of possible stem cells in theNCIh295R cell line.

Parathyroids

To analyze stem cells and CSC in parathyroids from patientswith hyperparathyroidism, Fang et al. examined parathyroidtissues from 20 patients with hyperparathyroidism usingfluorescence-activated cell sorting for the CD44/CD24 cellpopulation and immunohistochemistry [84]. They foundCD44-positive cells in abnormal glands but not in normalglands. They suggested that there was a resident neoplasticstem cell population from abnormal parathyroid glands inpatients with hyperparathyroidism [84].

Skin

Laga et al. used SOX2 expression to characterize embryonicneural crest stem cells in the skin [85]. They found rareSOX2 immunoreactive cells that also expressed cytokeratin20 or microphthalmia-associated transcription factor whichthey interpreted as being present in Merkel cells and inmelanocytic cells, respectively. Merkel cell carcinomas alsoexpressed nuclear SOX2 as did melanoma tumor cells frompatients with these malignancies. They advocated thatSOX2 may be a useful biomarker for subpopulations ofnormal skin cells that reside in established stem cell nichesthat may relate to Merkel cell and melanocyte ontogeny andtumor development [85].

Conclusions

Extensive studies of stem cells and CSCs have been done insome endocrine tissues such as the thyroid and the anteriorpituitary. Primary tumors as well as cell lines have beenstudied in thyroid tissues while mostly primary cells andtumors have been examined in the anterior pituitary. Manyof these studies have shown CSCs in these endocrine tu-mors. Isolation and characterization of CSCs in these endo-crine tumors have provided new insights about the biology


and pathophysiology of CSCs. A limited number of studiesof CSCs have been done in other endocrine tissues includinggastrointestinal carcinoids and islet cell tumors, tumors fromthe lung, adrenal cortex parathyroid and skin.

One of the major goals of CSCs studies is to discovertherapeutic targets that can effectively treat highly aggres-sive endocrine cancers, such as anaplastic thyroid carcino-ma, pituitary carcinomas, and adrenocortical carcinomas.With the rapid pace of progress in CSC research, this goalmay be attainable in the not too distant future.

Disclosure/Conflict of Interest The authors declare no conflict ofinterest.

References

1. De Lellis RA, Lloyd RV, Heitz PU, Eng C, editors. Pathologyand genetics of tumours of endocrine organs. Lyon: IARCPress, 2004.

2. Sipos JA, Mazzaferri EL. Thyroid cancer epidemiology and prog-nostic variables. Clin Oncol 22:395–404, 2010.

3. Weissman IL Stem cells: units of development, units of regenera-tion and units in evolution. Cell 100:157–168, 2000.

4. Thomson JA, Itskovitz-Eldor J, Shapiro SS, Waknitz MA,Swiergiel JJ, Marshall VS, Jones JM. Embryonic stem cell linesderived from human blastocysts. Science 282:1827, 1998.

5. Kern SE, Shibata D. The fuzzy math of solid tumor stem cells: aperspective. Cancer Res 67:8985–8, 2007.

6. Hoshi N, Kusakabe T, Taylor BJ, Kimura S. Side population cellsin the mouse thyroid exhibit stem/progenitor cell-like characteris-tics. Endocrinology 148:4251–8, 2007.

7. Ozaki T, Matsubara T, Seo D, Okamoto M, Nagashima K, SasakiY, et al. Thyroid regeneration: characterization of clear cells afterpartial thyroidectomy. Endocrinology 153:2514–25, 2012.

8. Klonisch T, Hoang-Vu C, Hombach-Klonisch S. Thyroid stemcells and cancer. Thyroid 19:1303–15, 2009.

9. Lin RY. Thyroid cancer stem cells. Nat Rev Endocrinol 7:609–16,2011.

10. Malaguarnera R, Morcavallo A, Giuliano S, Belfiore A. Thyroidcancer development and progression: emerging role of cancer stemcells. Minerva Endocrinol 37:103–15, 2012.

11. Fierabracci A. Identifying thyroid stem/progenitor cells: advancesand limitations. J Endocrinol 213:1–13, 2012.

12. Davies TF, Latif R, Minsky NC, Ma R. Clinical review: theemerging cell biology of thyroid stem cells. J Clin EndocrinolMetab 96:2692–702, 2011.

13. Thomas D, Friedman S, Lin RY. Thyroid stem cells: lessons fromnormal development and thyroid cancer. Endocr Relat Cancer15:51–8, 2008.

14. Malguarnera R, Morcavallo A, Giuliano S, Belfiore A. Thyroidcancer development and progression: emerging role of cancer stemcells. Minerva Endocrinol 37:103–115, 2012.

15. Lan L, Cui D, Nowka K, Derwahl M. Stem cells derived fromgoiters in adults form spheres in response to intense growth stim-ulation and require thyrotropin for differentiation into thyrocytes. JClin Endocrinol Metab 92:3681–8, 2007.

16. Fierabracci A, Puglisi MA, Giuliani L, Mattarocci S,Gallinella-Muzi M. Identification of an adult stem/progenitor

cell-like population in the human thyroid. J Endocrinol198:471–87, 2008.

17. Gómez-Gaviro MV, Lovell-Badge R, Fernández-Avilés F, Lara-Pezzi E. The vascular stem cell niche. J Cardiovasc Transl Res 5:618–630, 2012

18. Wang H, Zhang P, Liu L, Zou L. Hierarchical organization andregulation of the hematopoietic stem cell osteoblastic niche. CritRev Oncol Hematol 85(1):1–8, 2013

19. Cameselle-Teijeiro J, Febles-Pérez C, Sobrinho-Simões M.Papillary and mucoepidermoid carcinoma of the thyroid withanaplastic transformation: a case report with histologic and immu-nohistochemical findings that support a provocative histogenetichypothesis. Pathol Res Pract 191:1214–21, 1995.

20. Asioli S, Erickson LA, Lloyd RV. Solid cell nests in Hashimoto’sthyroiditis sharing features with papillary thyroid microcarcinoma.Endocr Pathol 20:197–203, 2009.

21. Aratake Y, Nomura H, Kotani T, Marutsuka K, Kobayashi K,Kuma K, Miyauchi A, Okayama A, Tamura K. Coexistent ana-plastic and differentiated thyroid carcinoma: an immunohisto-chemical study. Am J Clin Pathol 125:399–406, 2006.

22. Albores-Saavedra J, Hernandez M, Sanchez-Sosa S, Simpson K,Angeles A, Henson DE. Histologic variants of papillary and fol-licular carcinomas associated with anaplastic spindle and giant cellcarcinomas of the thyroid: an analysis of rhabdoid and thyroglob-ulin inclusions. Am J Surg Pathol 31:729–36, 2007.

23. Begum S, Rosenbaum E, Henrique R, Cohen Y, Sidransky D,Westra WH. BRAF mutations in anaplastic thyroid carcinoma:implications for tumor origin, diagnosis and treatment. ModPathol 17:1359–63, 2004.

24. Takano T, Amino N. Fetal cell carcinogenesis: a new hypothesis forbetter understanding of thyroid carcinoma. Thyroid 15:432–8, 2005.

25. Takano T. Fetal cell carcinogenesis of the thyroid: theory andpractice. Semin Cancer Biol 17:233–40, 2007.

26. Yang Z, Wang Z, Fan Y, Zheng Q. Expression of CD133 in SW620colorectal cancer cells is modulated by the microenvironment.Oncol Lett 4:75–79, 2012

27. Liu W, Wu L, Shen XM, Shi LJ, Zhang CP, Xu LQ, et al.Expression patterns of cancer stem cell markers ALDH1 andCD133 correlate with a high risk of malignant transformation oforal leukoplakia. Int J Cancer 132(4):868–74, 2013

28. Choi SA, Wang KC, Phi JH, Lee JY, Park CK, Park SH, et al. Adistinct subpopulation within CD133 positive brain tumor cellsshares characteristics with endothelial progenitor cells. CancerLett 324:221–30, 2012.

29. He H, Li MW, Niu CS. The pathological characteristics of gliomastem cell niches. J Clin Neurosci 19:121–7, 2012.

30. Ferrandina G, Petrillo M, Bonanno G, Scambia G. TargetingCD133 antigen in cancer. Expert Opin Ther Targets 13:823–37,2009.

31. Catalano V, Di Franco S, Lovino F, Dieli F, Stassi G, Todaro M.CD133 as a target for colon cancer. Expert Opin Ther Targets.16:259–67, 2012.

32. Silva IA, Bai S, McLean K, Yang K, Griffith K, Thomas D, et al.Aldehyde dehydrogenase in combination with CD133 definesangiogenic ovarian cancer stem cells that portend poor patientsurvival. Cancer Res 71:3991–4001, 2011.

33. Christgen M, Ballmaier M, Lehmann U, Kreipe H. Detectionof putative cancer stem cells of the side population phenotypein human tumor cell cultures. Methods Mol Biol 878:201–15,2012.

34. Britton KM, Eyre R, Harvey IJ, Stemke-Hale K, Browell D,Lennard TW, Meeson AP. Breast cancer, side population cellsand ABCG2 expression. Cancer Lett 323:97–105, 2012.

35. Al-Hajj M, Wicha MS, Benito-Hernandez A, Morrison SJ, ClarkeMF. Prospective identification of tumorigenic breast cancer cells.Proc Natl Acad Sci USA 100:3983–8, 2003.


36. Todaro M, Lovino F, Eterno V, Cammareri P, Gambara G, EspinaV, et al. Tumorigenic and metastatic activity of human thyroidcancer stem cells. Cancer Res 70:8874–85, 2010.

37. Reedijk M. Notch signaling and breast cancer. Adv Exp Med Biol727:241–57, 2012.

38. Reya T. and Clevers H. Wnt signaling in stem cells and cancer.Nature 434:843–50, 2005.

39. Alison MR, Lin WR, Lim SM, Nicholson LJ. Cancer stem cells: inthe line of fire. Cancer Treat Rev. 38:589–98, 2012.

40. Quail DF, Taylor MJ, Postovit LM. Microenvironmental regulationof cancer stem cell phenotypes. Curr Stem Cell Res Ther 7:197–216, 2012.

41. Prud’homme GJ. Cancer stem cells and novel targets for antitumorstrategies. Curr Pharm Des 18:2838–49, 2012

42. Mitsutake N, Iwao A, Nagai K, Namba H, Ohtsuru A, Saenko V, etal. Characterization of side population in thyroid cancer cell lines:cancer stem-like cells are enriched partly but not exclusively.Endocrinology 148:1797–803, 2007.

43. Zito G, Richiusa P, Bommarito A, Carissimi E, Russo L, CoppolaA, et al. In vitro identification and characterization of CD133(pos)cancer stem-like cells in anaplastic thyroid carcinoma cell lines.PLoS One 3:e3544, 2008.

44. Schweppe RE, Klopper JP, Korch C, Pugazhenthi U, Benezra M,Knauf JA, et al. Deoxyribonucleic acid profiling analysis of 40human thyroid cancer cell lines reveals cross-contaminationresulting in cell line redundancy and misidentification. J ClinEndocrinol Metab 93:4331–41, 2008.

45. Friedman S, Lu M, Schultz A, Thomas D, Lin RY. CD133+anaplastic thyroid cancer cells initiate tumors in immunodeficientmice and are regulated by thyrotropin. PLoS One 4:e5395, 2009.

46. Chen G, Xu S, Renko K, Derwahl M. Metformin inhibits growthof thyroid carcinoma cells, suppresses self-renewal of derivedcancer stem cells, and potentiates the effect of chemotherapeuticagents. J Clin Endocrinol Metab 97:E510–20, 2012.

47. Zhu W, Hai T, Ye L, Cote GJ. Medullary thyroid carcinoma celllines contain a self-renewing CD133+ population that is dependenton ret proto-oncogene activity. J Clin Endocrinol Metab 95:439–44, 2010.

48. Malguarnera R, Frasca F, Garozzo A, Giani F, Pandini G, Vella V, etal A. Insulin receptor isoforms and insulin-like growth factor receptorinhuman follicular cell precursors from papillary thyroid cancer andnormal thyroid. J Clin Endocrinol Metab 96:766–74, 2011

49. Liu J, Brown RE. Immunohistochemical detection ofepithelialmesenchymal transition associated with stemnessphenotype in anaplastic thyroid carcinoma. Int J Clin ExpPathol 3:755–62, 2010.

50. Thiery JP, Acloque H, Huang RY, Nieto MA. Epithelial–mesen-chymal transitions in development and disease. Cell 139:871–90,2009.

51. Mani SA, Guo W, Liao MJ, Eaton EN, Ayyanan A, Zhou AY, et al.The epithelial–mesenchymal transition generates cells with prop-erties of stem cells. Cell 133:704–15, 2008.

52. Yang J, Wenberg RA. Epithelial-mesenchymal transition: at thecrossroads of development and tumor metastasis. Dev Cell14:818–29, 2008.

53. Vasko V, Espinosa AV, Scouten W, He H, Auer H, LiyanarachchiS, et al. Gene expression and functional evidence of epithelial-to-mesenchymal transition in papillary thyroid carcinoma invasion.Proc Natl Acad Sci USA 104:2803–8, 2007.

54. Salerno P, Garcia-Rostan G, Piccinin S, Bencivenga TC, Di MaroG, Doglioni C, et al. TWIST1 plays a pleiotropic role in determin-ing the anaplastic thyroid cancer phenotype. J Clin EndocrinolMetab 96:E772–81, 2011.

55. Hardy RG, Vicente-Dueñas C, González-Herrero I, Anderson C,Flores T, Hughes S, et al. Snail family transcription factors are impli-cated in thyroid carcinogenesis. Am J Pathol 171:1037–46, 2007.

56. Buehler D, Hardin H, Shan W, et al. Expression of epithelial–mesenchymal transition regulators SNAIZ and TWIST1 in thyroidcarcinomas. Mod Pathol 2013 (In Press).

57. Liu S, Clouthier SG, Wicha MS. Role of microRNAs in theregulation of breast cancer stem cells. J Mammary Gland BiolNeoplasia 17:15–21, 2012.

58. Sheridan C, Kishimoto H, Fuchs RK, Mehrotra S, Bhat-NakshatriP, Turner CH, et al. CD44+/CD24- breast cancer cells exhibitenhanced invasive properties: an early step necessary for metasta-sis. Breast Cancer Res 8:R59, 2006.

59. Tsuji T, Ibaragi S, Hu GF. Epithelial-mesenchymal transition andcell cooperativity in metastasis. Cancer Res 69:7135–9, 2009.

60. Suga H, Kadoshima T, Minaguchi M, Ohgushi M, Soen M,Nakano , et al. Self-formation of functional adenohypophysis inthree-dimensional culture. Nature 480:57–62, 2011

61. Rizzoti K and Lovell-Badge R. Regenerative Medicine: organrecital in a dish. Nature 480:44–6, 2011.

62. Chen J, Gremeaux L, Fu Q, Liekens D, Van Laere S, VankelecomH. Pituitary progenitor cells tracked down by side populationdissection. Stem Cells 27:1182–95, 2009.

63. Vankelecom H. Non-hormonal cell types in the pituitarycandidating for stem cell. Semin Cell Dev Biol 18:559–70, 2007.

64. Vankelecom H, and Gremeaux L. Stem cells in the pituitarygland: a burgeoning field. Gen Comp Endocrinol 166:4788–88, 2010.

65. Castinetti F, Davis SW Brue T, Camper SA. Pituitary stem cellupdate and potential implications for treating hypopituitarism.Endocr Rev 32:453–71, 2011.

66. Fu Q, Gremeaux L, Luque M, Liekes D, Chen J, Buch T, et al. Theadult pituitary shows stem/progenitor cell activation in response toinjury and is capable of regeneration. Endocrinology 153:3224–35,2012.

67. Yamashita M, Qian ZR, Sano T, Horvath E, Kovacs K.Immunohistochemical study on so-called follicular cells andfolliculostellate cells in the human adenohypophysis. Pathol Int55:244–7, 2005.

68. Horvath E, Coire CI, Kovacs K, Smyth HS. Folliculo-stellate cellsof the human pituitary as adult stem cells: examples of theirneoplastic potential. Ultrastruct Pathol 34:133–9, 2012.

69. Florio T. Adult pituitary stem cells: from pituitary plasticity toadenoma development. Neuroendocrinology 94:265–77, 2011.

70. Fauquier T, Rizzoti K, Dattani M, Lovell-Badge R, Robinson IC.SOX2-expressing progenitor cells generate all of the major celltypes in the adult mouse pituitary gland. Proc Natl Acad Sci SA105:2907–12, 2008.

71. Wagner J, Lepore D, Thomas P. Differentiation of mouse embry-onic stem cells into growth hormone and prolactin expressing cellsin vitro. Mol Cell Endocrinol 273:68–74, 2007.

72. De Almeida JP, Sherman JH, Salvatori R, Quinones-Hinojosa A.Pituitary stem cells: review of the literature and current under-standing. Neurosurgery 67:770–80, 2010.

73. Inoue K, Mogi C, Ogawa S, Tomida S, Miyai S. Arefolliculo-stellate cells in the anterior pituitary gland supportivecells or organ-specific stem cells? Arch Physiol Biochem110:50–3, 2002.

74. Krylyshkina O, Chen J, Mebis L, Denef C, Vankelecom H.Nestin-immunoreactive cells in rat pituitary are neither hor-monal nor typical folliculo-stellate cells. Endocrinology146:2376–87, 2005.

75. Jin L, Tsumanuma I, Ruebel KH, Bayliss JM, Lloyd RVAnalysisof homogeneous populations of anterior pituitary folliculostellatecells by laser capture microdissection and reverse transcription-polymerase chain reaction. Endocrinology 142:1703–9, 2001.

76. Gleiberman AS, Ichurina T, Encinas JM, Roig JL, Krasnov P,Balordi F, et al. Genetic approaches identify adult pituitary stemcells. Proc Natl Acad Sci USA 105:6332–7, 2008.


77. Yunoue S, Arita K, Kawano H, Uchida H, Tokimura H,Hirano H. Identification of CD133+ cells in pituitary adeno-mas. Neuroendocrinology 94:302–12, 2011.

78. Xu Q, Yuan X, Tunici P, Liu G, Fan X, Xu M, et al. Isolation oftumour stem-like cells from benign tumours. Br J Cancer 101:303–11, 2009.

79. Gaur P, Sceusi EL, Samuel S, Xia L, Fan F, Zhou Y et al.Identification of cancer stem cells in human gastrointestinal carcinoidand neuroendocrine tumors. Gastroenterology 141:1728–37, 2011.

80. Jiang T, Collins BJ, Jin N, Watkins DN, Brock MV, Matsui W, et al.Achaete-scute complex homologue 1 regulates tumor-initiating ca-pacity in human small cell lung cancer. Cancer Res 69:845–54, 2009.

81. Sholl LM, LongKB,Hornick JL. Sox2 expression in pulmonary non-small cell and neuroendocrine carcinomas. Appl ImmunohistochemMol Morphol 18:55–61, 2010.

82. Simon DP, Hammer GD. Adrenocortical stem and progenitor cells:implications for adrenocortical carcinoma. Mol Cell Endocrinol351:2–11, 2012.

83. Lichtenauer UD, Shapiro I, Geiger K, Quinkler M, Fassnacht M,Nitschke R et al. Side population does not define stem cell-likecancer cells in the adrenocortical carcinoma cell line NCI h295R.Endocrinology 149:1314–22, 2008.

84. Fang SH, Guidroz JA, O’Malley Y, Lal G, Sugg SL, Howe JR, etal. Expansion of a cell population expressing stem cell markers inparathyroid glands from patients with hyperparathyroidism. AnnSurg 251:107–13, 2010.

85. Laga AC, Lai CY, Zhan Q, Huang SJ, Veazquez EF, Yang Q, et al.Expression of the embryonic stem cell transcription factor SOX2in human skin: relevance to melanocyte and merkel cell biology.Am J Pathol 176:903–13, 2010.

10 Endocr Pathol (2013) 24:1–10

stem cells and cancer stem-like cells in endocrine tissues

Documents