Neoplasia

Sakchai Chitpakdee, M.D.

ContentsIntroduction: Needs and Prospects for Cancer ControlEpidemiology of CancerNomenclatureCharacteristics of Benign and Malignant NeoplasmsCarcinogenesis : The Molecular Basis of CancerEtiology of Cancer: Carcinogenic AgentsHost Defense Against Tumors: Tumor ImmunityClinical Aspects of NeoplasiaLaboratory Diagnosis of CancerCancer Therapy, Prevention and Control

Introduction: Needs and Prospects for Cancer Control

Cancer is the second leading cause of death in the USCancer and heart disease are the major diseases and causes of death in old ageIncreased life expectancy and better clinical diagnosis has led to more cases of cancer being diagnosed, a proportion of which would have previously been missed.There has undoubtedly been a real increase in the number of people who develop cancer due to an increased exposure to etiological agents.

Cancer is not a modern diseaseA tumour has been reported from the tail of a dinosaur; a true malignant tumour? or a callous of bone?The femur of a homo erectus (Pithecanthropus) dating from 450 000 BC initially gave the appearance of a tumour but likely to have been myositis ossificansA lesion found in the calvarium of a skeleton from the Twentieth Dynasty of Ancient Egypt (c. 1200 BC) exhibits malignant destruction of the jaw, sinus and palateWritings from ancient India (Ayuruedic books) suggest that cancer was able to be diagnosed correctly over 2500 years ago but was considered incurable. Tumours of the oral cavity, pharynx, oesophagus, pelvis and rectum are described

Global cancer burdenIn 2008, there were 12.4 million new cancer cases and 7.6 million cancer deaths worldwide (60%)Lung cancer burden, in terms of incidence and mortality, is among the highest in the worldMore than half of cancer cases and 60% of deaths occur in the less-developed countriesThere are striking variations of cancer patterns by site from region to regionFuture cancer burden will be influenced by trends in the elderly population of both the less-developed and more-developed areasThe role of prevention in cancer control programmes (tobacco control, vaccination, screening) will increase in the coming decades

Epidemiology of cancerThe incidence of cancer varies with age, race, geographic factors, and genetic backgrounds.Cancers are most common at the two extremes of age.The geographic variation results mostly from different environmental exposures.Most cancers are sporadic, but some are familial. Predisposition to hereditary cancers may be autosomal dominant or autosomal recessive. The former are usually linked to inheritance of a germ-line mutation of cancer suppressor genes, whereas the latter are typically associated with inherited defects in DNA repair.Familial cancers tend to be bilateral and arise earlier in life than their sporadic counterparts.

NomenclatureNeoplasia = “new growth” “The development of neoplasms” [neo-, neos = new][+plassein = to form]

Neoplasm = “A new and abnormal formation of tissue, as a tumor or growth” [+plasma = form, mold]

Tumor = “A swelling” “neoplasm”

Oncology = “The study of tumors” [oncos = bulk, mass]

Benign vs. Malignant tumor = “ ไมรายแรง ” “ รายแรง หรือ มะเร็ง ”

Cancer = Malignant neoplasm [Karnikos = crab]

Definition of NeoplasmWillis:

“A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues and persists in the same excessive manner after cessation of the stimuli which evoked the change”

Fundamental to the origin of neoplasms

Basic components of tumors

TerminologyBenign tumors (suffix -oma)

Mesenchymal tissue fibroma (fibrous), chondroma (cartilage)Glandular epithelium adenoma, cystadenoma (cystic mass)Squamous & transitional epithelium acanthoma, papilloma (finger-like fronds)

Malignant tumors (suffix –sarcoma, -carcinoma, or prefix with malignant)

Epithelium carcinoma (general), adenocarcinoma (glandular), Mesenchymal tissue fibrosarcoma (fibrous)Others malignant lymphoma, malignant melanoma

Terminology (continued)Tumors with mixed component = mixed tumors

e.g. pleomorphic adenoma (salivary gland), fibroadenoma (breast)

Teratoma totipotent stem cells (germ layers)Mature vs. immature teratoma

Malignant tumors : lymphoma, melanoma, seminoma, hepatoma, mesothelioma

Tumor-like massHamartoma = mass of disorganized indigenous tissueChoristoma (heterotopic rest) = ectopic tissue

Characteristics of Benign and Malignant Neoplasms

Differentiation and AnaplasiaThe extent of resemblance of the parenchymal cells to their normal original cells morphologically and functionally

Well differentiated moderately poorly differentiatedUndifferentiated (lack of differentiation) = anaplasiaDedifferentiated (loss of differentiation)Benign tumors (well differentiated)Malignant tumors (well differentiated to anaplasia)

Anaplastic cells: pleomorphism, hyperchromatic, bizarre nuclei, numerous mitoses, atypical mitosisDysplasia : loss in the uniformity of cells and their architectural orientation (non-neoplastic)

Rate of growth and extensionBenign tumors: slowly grow, localized, form capsule, not invade, and not metastasize

Malignant tumors: fast grow, infiltrate, invade, and metastasize

Poorly differentiated tumor rapidly grow

Metastasis = development of secondary implantsMalignant tumors metastasis and local invasionAnaplastic and large tumor likely metastasis1) seeding within body cavities 2) lymphatic 3) hematogenous

Carcinogenesis : The molecular basis of cancer

Nonlethal genetic damage (mutation) lies at the heart of carcinogenesis

Tumor mass : clonal expansion of a single progenitor cells that has incurred genetic damage

Tumor = monoclonal

Regulatory genes targeting for genetic damageProto-oncogenesTumor suppressor genesGenes regulating apoptosisGenes involving DNA repair

Alterations for malignant transformation

Self-sufficiency in growth signals (oncogenes)Insensitivity to growth-inhibitory signals (tumor suppressor genes)Evasion of apoptosisLimitless replicative potentialSustained angiogenesisAbility of invade and metastasisDefects in DNA repair (mutator phenotype)Escape from immune attack

Self-sufficiency in Growth signals

OncogenesOncogenes can promote uncontrolled cell proliferation by several mechanisms: Stimulus-independent expression of growth factor and its receptor, setting up an autocrine loop of cell proliferation

PDGF-PDGF-receptor in brain tumors Mutations in genes encoding growth factor receptors, leading to overexpression or constitutive signaling by the receptor (e.g., EGF receptors)

EGF-receptor family members, including HER2/NEU (breast, lung, and other tumors)

Mutations in genes encoding signaling molecules RAS mutations (15-20% of all tumors)Fusion of ABL tyrosine kinase with BCR protein in certain leukemias generates a hybrid protein with constitutive kinase activity

OncogenesOverproduction or unregulated activity of transcription factors

Translocation of MYC in some lymphomas leads to overexpression and unregulated expression of its target genes controlling cell cycling and survival

Mutations that activate cyclin genes or inactivate normal regulators of cyclins and cyclin-dependent kinases

Complexes of cyclins with cyclin-dependent kinases (CDKs) drive the cell cycle by phosphorylating various substratesCDKs are controlled by inhibitors;Mutations in genes encoding cyclins, CDKs, and CDK inhibitors result in uncontrolled cell cycle progressionSuch mutations are found in wide variety of cancers including melanomas, brain, lung, and pancreatic cancer.

Insensitivity to Growth-Inhibitory SignalsTumor suppressor genes encode proteins that inhibit cellular proliferation by regulating the cell cycle. Both copies of the gene must be lost for tumor development, leading to loss of heterozygosity (LOH) at the gene locus.In cases with familial predisposition to develop tumors, the affected individuals inherit one defective (nonfunctional) copy of a tumor suppressor gene and lose the second one through somatic mutation. In sporadic cases both copies are lost through somatic mutations.

Insensitivity to Growth-Inhibitory SignalsRB Gene and Cell Cycle

RB exerts antiproliferative effects by controlling the G1-to-S transition of the cell cycle. In its active form RB is hypophosphorylated and binds to E2F transcription factor. This interaction prevents transcription of genes like cyclin E that are needed for DNA replication, and so the cells are arrested in G1.Growth factor signaling leads to cyclin D expression, activation of the cyclin D-CDK4/6 complexes, inactivation of RB by phosphorylation, and thus release of E2F.Almost all cancers will have disabled the G1 checkpoint, by mutation of either RB or genes that affect RB function, like cyclin D, CDK4, and CDKIs.Many oncogenic DNA viruses, like HPV, encode proteins (e.g., E7) that bind to RB and render it nonfunctional.

Insensitivity to Growth-Inhibitory Signalsp53 Gene: Guardian of the Genome

p53 is the central monitor of stress in the cell and can be activated by anoxia, inappropriate oncogene signaling, or DNA damage. Activated p53 controls the expression and activity of genes involved in cell cycle arrest, DNA repair, cellular senescence, and apoptosis.DNA damage leads to activation of p53 by phosphorylation. Activated p53 drives transcription of CDKN1A (p21) that prevents RB phosphorylation and therefore causes a G1-S block in the cell cycle. This pause allows the cells to repair DNA damage.

Insensitivity to Growth-Inhibitory Signalsp53 Gene: Guardian of the Genome (continued)

If DNA damage cannot be repaired, p53 induces cellular senescence or apoptosis.Of human tumors, 70% have homozygous loss of p53.Patients with the rare Li-Fraumeni syndrome inherit one defective copy in the germ line and lose the second one in somatic tissues; such individuals develop a variety of tumors.As with RB, p53 can be incapacitated by binding to proteins encoded by oncogenic DNA viruses like HPV (E6), and possibly EBV and HBV.

Evasion of ApoptosisApoptosis can be initiated through the extrinsic or intrinsic pathways.Both pathways result in the activation of a proteolytic cascade of caspases that destroys the cell.Mitochondrial outer membrane permeabilization is regulated by the balance between pro-apoptotic (e.g., BAX, BAK) and anti-apoptotic molecules (BCL2, BCL-XL). BH-3-only molecules activate apoptosis by tilting the balance in favor of the pro-apoptotic molecules.In 85% of follicular B-cell lymphomas the anti-apoptotic gene BCL2 is activated by the t(8;14) translocation.

Limitless Replicative PotentialIn normal cells, which lack expression of telomerase, the shortened telomeres generated by cell division eventually activate cell cycle checkpoints, leading to senescence and placing a limit on the number of divisions a cell may undergo.In cells that have disabled checkpoints, DNA repair pathways are inappropriately activated by shortened telomeres, leading to massive chromosomal instability and mitotic crisis.Tumor cells reactivate telomerase, thus staving off mitotic catastrophe and achieving immortality.

Development of Sustained AngiogenesisVascularization of tumors is essential for their growth and is controlled by the balance between angiogenic and anti-angiogenic factors that are produced by tumor and stromal cells.Hypoxia triggers angiogenesis through the actions of HIF1α. Because of its ability to degrade HIF1α and thus prevent angiogenesis, VHL acts as a tumor suppressor gene. Many other factors regulate angiogenesis; for example, p53 induces synthesis of the angiogenesis inhibitor thrombospondin-1.

Ability to Invade and MetastasizeAbility to invade tissues, a hallmark of malignancy, occurs in four steps: loosening of cell-cell contacts, degradation of ECM, attachment to novel ECM components, and migration of tumor cells.Cell-cell contacts are lost by the inactivation of E-cadherin through a variety of pathways.Basement membranes and interstitial matrix degradation is mediated by proteolytic enzymes secreted by tumor cells and stromal cells, such as MMPs and cathepsins.Proteolytic enzymes also release growth factors sequestered in the ECM and generate chemotactic and angiogenic fragments from cleavage of ECM glycoproteins.

Ability to Invade and MetastasizeThe metastatic site of many tumors can be predicted by the location of the primary tumor. Many tumors arrest in the first capillary bed they encounter (lung and liver, most commonly).Some tumors show organ tropism, probably due to expression of adhesion or chemokine receptors whose ligands are expressed by the metastatic site.

Genomic Instability –Enabler of MalignancyIndividuals with inherited mutations of genes involved in DNA repair systems are at a greatly increased risk of developing cancer.Patients with HNPCC syndrome have defects in the mismatch repair system and develop carcinomas of the colon. These patients show microsatellite instability (MSI), in which short repeats throughout the genome change in length.Patients with xeroderma pigmentosum have a defect in the nucleotide excision repair pathway and are at increased risk for the development of cancers of the skin exposed to UV light, because of an inability to repair pyrimidine dimers.

Genomic Instability –Enabler of MalignancySyndromes involving defects in the homologous recombination DNA repair system compose a group of disorders (Bloom syndrome, ataxia-telangiectasia, and Fanconi anemia) that are characterized by hypersensitivity to DNA-damaging agents, such as ionizing radiation. BRCA1 and BRCA2, which are mutated in familial breast cancers, are involved in DNA repair.

Molecular Basis of Multistep Carcinogenesis

Karyotypic changes in TumorsTumor cells may develop a variety of nonrandom chromosomal abnormalities; these include balanced translocations, deletions, and gene amplification.Balanced translocations contribute to carcinogenesis by overexpression of oncogenes or generation of novel fusion proteins with altered signaling capacity. Deletions frequently affect tumor suppressor genes, whereas gene amplification increases the expression of oncogenes.Tumor suppressor genes and DNA repair genes may also be silenced by epigenetic changes, which involve reversible, heritable changes in gene expression that occur, not by mutation, but by methylation of the promoter.

miRNA and cancersmiRNA = small noncoding SS-RNAs, approximately 22 nucleotides in length, incorporated into the RNA-induced silencing complex (post-transscriptional gene silencing)Control cell growth, differentiation, and cell survivalChanges in expression in cancer cells: amplication and deletion of miRNA lociTarget gene if oncogene miRNA act as TS genes; if TS genes miRNA act as oncogenemiRNA profiling classification of tumor

Etiology of Cancer: Carcinogenic Agents

Chemical carcinogensChemical carcinogens have highly reactive eletrophile groups that directly damage DNA, leading to mutations and eventually cancer.Direct-acting agents do not require metabolic conversion to become carcinogenicIndirect-acting agents are not active until converted to an ultimate carcinogen by endogenous metabolic pathways. Polymorphisms of endogenous enzymes like cytochrome P-450 may influence carcinogenesis.

Chemical carcinogensFollowing exposure of a cell to a mutagen or an initiator, tumorigenesis can be enhanced by exposure to promoters, which stimulate proliferation of the mutated cells.Examples of human carcinogens include direct-acting (e.g., alkylating agents used for chemotherapy), indirect-acting (e.g., benzopyrene, azo dyes, and aflatoxin), and promoters/agents that cause pathologic hyperplasias of liver, endometrium.

Radiation CarcinogenesisIonizing radiation causes chromosome breakage, translocations, and, less frequently, point mutations, leading to genetic damage and carcinogenesis.UV rays induce the formation of pyrimidine dimers within DNA, leading to mutations. Therefore UV rays can give rise to squamous cell carcinomas, basal cell carcinoma and melanomas of the skin.

Oncogenic VirusesHTLV-1 causes a T-cell leukemia that is endemic in Japan and the Caribbean.HPV has been associated with benign warts, as well as cervical cancer.The oncogenic ability of HPV is related to the expression of two viral oncoproteins, E6 and E7; they bind to p53 and RB, respectively, neutralizing their function; they also activate cyclins.E6 and E7 from high-risk HPV (that give rise to cancers) have higher affinity for their targets than E6 and E7 from low-risk HPV (that give rise to low-grade tumors).

Oncogenic VirusesEBV has been implicated in the pathogenesis of Burkitt lymphomas, lymphomas in immunosuppressed individuals with HIV infection or organ transplantation, some forms of Hodgkin lymphoma, and nasopharyngeal carcinoma. All except the nasopharyngeal cancers are B-cell tumors.Certain EBV gene products contribute to oncogenesis by stimulating a normal B-cell proliferation pathway.Concomitant compromise of immune competence allows sustained B-cell proliferation and eventually development of lymphoma with occurrence of additional mutations such as t(8 ; 14), leading to activation of the MYC gene.KSHV/HHV-8 is associated with Kaposi’s sarcoma

Hepatitis B and Hepatitis C VirusesBetween 70% and 85% of hepatocellular carcinomas worldwide are due to infection with HBV or HCV.The oncogenic effects of HBV and HCV are multifactorial, but the dominant effect seems to be immunologically mediated chronic inflammation, hepatocellular injury, stimulation of hepatocyte proliferation, and production of reactive oxygen species that can damage DNA.The HBx protein of HBV and the HCV core protein can activate a variety of signal transduction pathways that may also contribute to carcinogenesis.

Helicobacter pylori (H. pylori)H. pylori infection has been implicated in both gastric adenocarcinoma and MALT lymphoma.The mechanism of H. pylori-induced gastric cancers is multifactorial, including immunologically mediated chronic inflammation, stimulation of gastric cell proliferation, and production of reactive oxygen species that damage DNA. It is thought that H. pylori infection leads to polyclonal B-cell proliferations and that eventually a monoclonal B-cell tumor (MALT lymphoma) emerges as a result of accumulation of mutations.

Host defense against tumorsTumor antigens

Tumor-specific antigens: only present on tumor cellsTumor-associated antigens: present on both tumor and normals cells

Main classes of tumor antigens:Products of mutated oncogenes and tumor suppressor genesProducts of other mutated genesOverexpressed or aberrantly expressed cellular proteinsTumor antigens produced by oncogenic virusesOncofetal antogens: CEA, alpha-fetoproteinAltered cell surface glycolipids and glycoproteins: CA-125, CA19-9

Cell Type-Specific Differentiation antigensSpecific for particular lineages or differentiation stages of various cell typesPotential targets for immunotherapy and for identifying the tissue of origin if tumors (immunohistochemistry)CD10 and CD20 are surface markers for B-cell-derived tumors, antibodies against CD20 are used for B-cell lymphoma chemotherapyExample of cellular marker for tumors: CD3 (T-cell), CD20 (B-cell), cytokeratin (carcinoma), HMB-45 (melanoma), CD31 (endothelium), desmin (muscle)

Immune surveillenceTumor cells can be recognized by the immune system as non-self and destroyed.Antitumor activity is mediated by predominantly cell-mediated mechanisms. Tumor antigens are presented on the cell surface by MHC class I molecules and are recognized by CD8+ CTLs.The different classes of tumor antigens include products of mutated proto-oncogenes, tumor suppressor genes, overexpressed or aberrantly expressed proteins, tumor antigens produced by oncogenic viruses, oncofetal antigens, altered glycolipids and glycoproteins, and cell type-specific differentiation antigens.

Immune SurveillanceImmunosuppressed patients have an increased risk of cancer.In immunocompetent patients, tumors may avoid the immune system by several mechanisms, including

selective outgrowth of antigen-negative variants, loss or reduced expression of histocompatibility antigens, and immunosuppression mediated by secretion of factors (e.g., TGF-β) from the tumor.

Clinical aspects of neoplasiaLocation and impingment on adjacent structuresFunctional activity such as hormone synthesis or the development of paraneoplastic syndromesBleeding and infections when the tumor ulcerates through adjacent surfacesSymptoms that result from ruptured or infarctionCachexia or wasting

Clinical aspects of tumorsCachexia, defined by progressive loss of body fat and lean body mass, accompanied by profound weakness, anorexia, and anemia, is caused by release of cytokines (IL-1, TNF) by the tumor or host.Paraneoplastic syndromes, defined by systemic symptoms that cannot be explained by tumor spread or by hormones appropriate to the tissue, are caused by the ectopic production and secretion of bioactive substances, such as ACTH, PTHrP, or TGF-α.

Grading and StagingGrading of tumors is determined by cytologic appearance and is based on the idea that behavior and differentiation are related, with poorly differentiated tumors having more aggressive behavior. (Grade I-IV; high- or low-grade)Staging, determined by surgical exploration or imaging, is based on size, local and regional lymph node spread, and distant metastases. Staging has greater clinical value than grading.

AJC (American Joint Committee): Stage I-IVTNM (T = primary tumor; N = regional lymph nodes; M = metastases)

Laboratory Diagnosis of cancers: Morphological methods

Histology of tissueTissue biopsy: Incisional biopsy and Excisional biopsyTissue processes : Frozen and paraffin sectionTumor classification and grading : WHO classification (WHO blue books): morphology code (ICD-O)

Cytology of smear or fluidFine-needle aspirations: breast, thyroid, lymph nodes, salivary glandsExfoliative specimens:

Papanicolaou (PAP) smear: cervicovaginal smearBody fluid: ascites, pleural effusion

Tumor markersImmunohistochemistry and flow cytometry help in the diagnosis and classification of tumors, because distinct protein expression patterns define different entities.Proteins released by tumors into the serum, such as PSA, can be used to screen populations for cancer and to monitor recurrence following treatment.

Molecular DiagnosisMolecular analyses are used to determine diagnosis, prognosis, the detection of minimal residual disease, and the diagnosis of hereditary predisposition to cancer.Molecular profiling of tumors by cDNA arrays can determine expression of large segments of the genome at once and can be useful in molecular stratification of otherwise identical tumors for the purpose of treatment and prognostication.

Principles of cancer therapySurgeryChemotherapyRadiotherapySupportive and palliative care

Medical OncologyThere are 20–30 cytotoxic drugs commonly used in the treatment of malignant diseaseThese drugs are often administered in combination, using multiple mechanisms to induce cancer cell deathCytotoxic drugs can be associated with a range of side effects (neutropenia, oral ulceration, diarrhoea, hair loss, and nerve and kidney damage)Chemotherapy has significantly improved survival of breast, colorectal, testicular and ovarian cancer, sarcoma and a range of haematological malignanciesMolecular biological insights have given us a range of new targets based on growth factors and their receptors which have already begun to yield new drugs

Cancer Prevention and ControlSurveillancePrimary preventionSecondary preventionDiagnosis and treatmentPalliative care

ReferencesWorld Cancer Report 2008 : WHO IARCHospital-based Cancer Registry 2007: National Cancer Institute, Thailand Robbins Basic Pathology, 8th edition