Gastrointestinal tract spindle cell lesions -

histological and molecular features

Luigi Terracciano

Staffmeeting 23.1.2019

GIST

Epidemiology

• 1 case / 100.000 / year (GISTs clinical significant, >2 cm)

• Micro GISTs (< 1cm) are quite common. Autopsy studies up to

22.5% (Agaimy A, Am J Surg Pathol, 2007)

• From children to elderly (64ys median age)

• Equal sex distribution (in children >> female)

• > Sporadic; rarely in tumor syndromes

• Stomach (60%), jejunum and ileum (30%), duodenum (5%), colon

&rectum (< 5%). Rarely in esophagus, appendix and gallbladder

• E-GISTs: omentum, mesentery, retroperitoneum and perineum

Macroscopic Findings

• From 1 mm to > 20 cm

• Median size: stomach 6 cm, duodenum

4.5 cm, jejunum / ileum 7 cm

• Well-circumscribed solitary lesion,

centered on the wall of the gut

• Rarely, multiple lesions in the stomach

(> pediatric and micro GISTs) or in the

small bowel (> familial GISTs and GISTs

associated with neurofibromatosis)

• Frequently ulcerate the overlying

mucosa

• Tan and fleshy with frequent cystic

changes and hemorrhage

Microscopic Findings

Spindle cell (70%) Epithelioid (20%)

Minimal cytologic atypia Neuroendocrine or „paraganglioma“

like-features

Immunohistochemical Findings

• KIT (CD117): nearly 95% of cases (cytoplasmic, membranous, dot-like

perinuclear). Highly sensitive but relatively low specific (> melanomas!)

5% negative (> PDGFRa mutant GISTs)

• DOG1: (discovered on GIST1, ANO1): very sensitive and more specific,

positive also in KIT –ve GISTs

• CD34: 70% of cases

• H-caldesmon : 60-70%

• Smooth muscle actin: 30-40%

• S-100: 5%

• Desmin, cytokeratin: 2%

CD117 DOG1

SMA S100

TUMOR PARAMETERS RISK OF PROGRESSIVE DISEASE* (%), BASED ON SITE OF ORIGIN

Mitotic Rate

Size Gastric Duodenum Jejunum/Ileum (and EGISTs)

Rectum

≤5 per 50 HPF (5 mm2)

≤2 cm None (0%) None (0%) None (0%) None (0%)

>2, ≤5 cm Very low (1.9%) Low (8.3%) Low (4.3%) Low (8.5%)

>5, ≤10 cm Low (3.6%) (Insuff. data) Moderate (24%) (Insuff. data)

>10 cm Moderate (10%) High (34%) High (52%) High (57%)

>5 per 50 HPF (5 mm2)

≤2 cm None** (Insuff. data) High** High (54%)

>2, ≤5 cm Moderate (16%) High (50%) High (73%) High (52%)

>5, ≤10 cm High (55%) (Insuff. data) High (85%) (Insuff. data)

>10 cm High (86%) High (86%) High (90%) High (71%)

Histological risk factors for conventional GISTs AFIP and College of American Pathologists

Miettinen M, Lasota J, Semin Diagn Pathol, 2006

RISK CATEGORY TUMOR SIZE (cm) MITOTIC INDEX (PER 50 HPFs)

PRIMARY TUMOR SITE

Very low risk

<2.0 ≤5 Any

Low risk 2.1-5.0 ≤5 Any

Intermediate risk 2.1-5.0 >5 Gastric

<5.0 6-10 Any

5.1-10.0 ≤5 Gastric High risk Any Any Tumor rupture

>10.0 Any Any

Any >10 Any

>5.0 >5 Any

2.1-5.0 >5 Nongastric

5.1-10.0 ≤5 Nongastric

Histological risk factors for conventional GISTs

II Joensuu Criteria

Joensuu H, Hum Pathol, 2008

Joensuu H, Lancet Oncol, 2012

Additional morphological criteria: coagulative necrosis, mucosal invasion,

ulceration, proximal location in stomach versus antrum.

Frequency of the molecular GIST subtypes

Schematic representation of KIT and PDGFRA with main

mutational hotspots

Cioffi A & Moki RG, J Clin Oncol, 2015

KIT Exon 11:

• Interstitial deletions between

codons 550-579 (> 557 and

579 codons)

• Point mutations (> 557, 559,

560 and 576 codons)

• Tandem duplications between

571 and 591 (> gastric GISTs )

Exon 9:

• Duplication of codons 502-503

(small intestine GISTs and >

malignancy)

Exons 13 and 17:

• Point mutations

PDGFRA

• > gastric locations and

epithelioid morphology

• D842V mutation is the most

frequent (56-75%)

Chr 4q12

ATP-binding region

Activation loop

RTK Mutations Localisation

KIT Exon 9 > Small bowel, PDGFRA >> Stomach

Histology

PDGFRA and WT : epithelioid

Prognosis

– KIT exon 9: better relapse free survival after curative resection

– However less benefit from imatinib in adjuvant and metastatic settings : Higher dosis ? Data conflicting !

– Clinical benefit of second line sunitinib

– KIT exon 11 deletions higher risk of relapse (> 557 and 558 del.). → Reclassification of

gastric GISTs of intermediate prognosis as high risk with respect to relapse (Martin-Broto J,

Ann Oncol, 2010, Corless CL, J Clin Oncol, 2014).

– In the metastatic setting confer an exquisity sensitivity to imatinib (Heinrich MC, J Clin Oncol,

2003)

– PDGFRA often indolent (> Exon 18, D842V), > resistance to imatinib, sunitinib and nilotinib. Crenolanib ?

„Wild type“ GIST

• 10-15% without any mutation of KIT and PDGFRA

genes. Too broad and non-specific.

• Young patients

• Lymph node metastasis is frequent

• TKIs are not effective

• Risk stratification should not be used in SDH-deficient

GISTs

„Wild type“ GIST

Succinate Dehydrogenase Deficient GIST

• 42% of wild-type GISTs, 3% of all GISTs, 7,5% of stomach GISTs

• > Gastric location, epithelioid or mixed morphology, multinodular / infiltrative

growth pattern, multifocal, strongly KIT +, loss of SDHB immunohistochemical

expression (27% also lack of SDHA)

• Propensity of lymph node and liver metastasis (50%), but indolent behaviour

• Carney triad: loss of SDHB may be due to hypermethylation of the promoter

region of the SDHB gene

• Carney-Stratakis syndrome: germline

mutations of SDH subunits A, B, C and D

McWhinney SR, N Engl J Med, 2007

Histology of SHD deficient GISTs

SDHB SDHA

SDHB SDHA

DOG1

DOG1

Posttreatment changes

• Most GISTs show some histopathologic response to imatinib, but this is usually incomplete

and does not correlate with clinical or radiologic response

• Necrosis and / or hyalinization; cystic changes, haemorrhage, hypocellularity and

myxohyaline stroma

• Possible loss of CD117 and CD34 positivity ; DOG1 better retained

• Cytological phenotypic changes and possible acquisition of myoid phenotype

Pauwels P, Histopathology, 2005

Liegl B, Am J Surg Pathol, 2009

Rare Mesenchymal Tumors of Gastrointestinal

Tract

• Malignant Gastrointestinal Neuroectodermal Tumor (GNET)

• Synovial Sarcoma

• Kaposi Sarcoma

• Perivascular Epitheliod Cell Tumor

• Leiomyosarcoma

• Malignant peripheral nerve sheat tumor (MPNST)

• Inflammatory myyofibroblastic tumor

• Plexiform fibromyxoma

Gastrointestinal tract spindle cell lesions

Just like real estate, it‘s all about location!

Mucosa to serosa

• Differential Diagnosis: noting whether a tumor is centered in the mucosa,

submucosa, muscularis propria or serosa

• Each type of lesions is often restricted to one of these layers

Voltaggio L, Mod Pathol, 2015

Location of mesenchymal lesions in the GI tract by layer I

Lesion Favored site in the GI tract

Malignant potential

Mucosa Submucosa Muscularis propria

Mesentery

Benign epithelioid nerve sheath tumors

Colon Benign X

Sporadic ganglioneuroma

Colon Benign X

Psammomatous melanotic schwannoma

Esophagus, colon, stomach

Likely benign X

Begnin fibroblastic polyp/perineuroma

Colon Benign X

Leiomyoma Colon Benign

X(associated with muscolaris mucosae)

Kaposi sarcoma Stomach Quasi-neoplastic-related to immune suppression

X

Inflammatory fibroid polyp

Stomach (antrum)

Benign X

Synovial sarcoma

Stomach Malignant X X X

Gangliocytic paragaglioma

Duodenum Low grade-lymph nodes metastases reported

X X

Glomus tumor Stomach Usually benign X

Plexiform fibromyxoma

Stomach Benign X

Location of mesenchymal lesions in the GI tract by layer II

Lesion Favored site in the GI tract

Malignant potential

Mucosa Submucosa Muscularis propria

Mesentery

GIST Stomach Variable X

Gastrointestinal schwannoma

Stomach Benign X

Leiomyoma Esophagus Benign X

Malignant GNET Colon Malignant X

Leiomyosarcoma Colon Malignant

X

Ganglioneuroma- tosis

Colon Benign X X X X

Mesenteric fibromatosis

Small intestine

Benign, local aggressive

X X

Inflammatory myofibroblastic tumor

Small intestine

Variable X X

Sclerosing mesenteritis

Small intestine

Benign X

IgG4-related fibrosclerosing diasease

Small intestine

Benign X

Heterotopic myosistis ossificans

Small intestine

Benign X

Malignant Gastrointestinal Neuroectodermal

Tumor (GNET)

• Also known as gastrointestinal clear cell sarcoma-like tumor

• Around 50 reported cases, increasingly recognized

• Young to middle–aged adults

• Mean age 40 years

• Small bowel (70%), stomach, colon,

• Large infiltrative masses

• Aggressive sarcoma lymph node and liver metastases

Stockman DL, Am J Surg Pathol, 2012

Malignant Gastrointestinal Neuroectodermal

Tumor (GNET)

• Different from conventional clear cell

sarcoma of tendons and

aponeuroses

• Sheet-like, alveolar, pseudopapillary

• Rounded/epithelioid >>spindle cells

• Eosinophilic to clear cytoplasm

• Small nucleoli uniform cytology

• Some tumors with prominent

osteoclast-like giant cells

GNET Histology

Stockman DL, Am J Surg Pathol, 2012

Malignant Gastrointestinal Neuroectodermal

Tumor (GNET): Immunophenotype and Genetics

• Diffuse strong reactivity for S-100 and SOX10

• Lacks melanocytic markers (HMB45, melan-A, MiTF)

• t (12;22) with ATF1-EWSR1

t (2;22) with CREB1-EWSR1

• Diagnosis can be confirmed by FISH

• Aggressive behavior with frequent

lymph nodes and liver metastases

EWSR1

ATF1

Gastrointestinal smooth muscle tumors

Leiomyoma: all segments of GI tract

- mural (> esophagus, 5 times > GIST, but 1:50 in

stomach and small intestine)

- muscularis mucosae (> colon and rectum)

- younger patients than GIST

- > sporadic; Alport syndrome, MEN type1

Cytoplasmic globoid inclusions, desmin + Cave: some GI leiomyomas can be

colonized by KIT+ Cajal cells

Leiomyosarcoma

• Very rare tumor (around 1:50 of GIST)

• After 2000, around 70 reported cases

• Wide age range (18-94 years, median 60 years)

• Small bowel (1 for 30 GISTs), colon, anorectum, stomach and

esophagus (extremely rare)

• Large, bulky tumors (average site > 10 cm); > polypoid growth in

rectum

• Ulceration of the overlying mucosa is common

• Frequent liver and lung metastases; tumor size (≥ 5 cm) indicator

of poor prognosis; smaller tumors have a relatively better

prognosis than GISTs with similar mitotic rates

Yamamoto H, Histopathology, 2013

Morphology

• Histology: spindle

cells, eosinophlic

fibrillary cytoplasm,

cigar-shaped nuclei with

blunt end

• High mitotic rate (>20 /

50 HPF)

•SMA, desmin and

caldesmon +ve ;CD117

and DOG-1 -ve

Epstein-Barr Virus-associated Smooth

Muscle Tumors

Miettinen M, Modern Pathol, 2014

• A rare subset of smooth-muscle tumors in immunosuppressed patients (> AIDS,

solid organ transplant patients)

• Tumor multiplicity is common

• Behavior indolent and unpredictable: mitotic rate not a reliable marker of

malignancy

Synovial Sarcoma

Romeo S, Clin Sarcoma Res, 2015

• Male:female = 3:1

• Age range 17-61 (median 44 ys)

• Stomach, esophagus, small intestine, colon. Size: 2-15 cm (median 8 cm)

• Stomach : mainly monophasic SS, intramural,

Esophagus: Biphasic SS, endophytic

Immunohistochemistry: cytokeratins, EMA and vimentin. CD99, bcl2,TLE1 S-100.

Cave : focal positivity for DOG 1

• FISH: t (X;18) (p11;q11) SS18 (SYT) gene, SSX1, SSX2, SSX4 genes

• Variable prognosis (grading, size)

Synovial Sarcoma

Romeo S, Clin Sarcoma Res, 2015

Thank you for your attention!

Therapy and resistence

• Median overall survival in patients with metastatic GIST:

Before TKIs administration: 20 months (De Matteo RP, Ann Surg, 2000)

After TKIs adminstration: > 5 years (Blanke CD, J Clin Oncol, 2008)

• Roughly 60% of GISTs never experience a relapse and are considered cured

only by surgery

• Localized disease:

• High-risk GISTs: adjuvant therapy of 400mg /day imatinib mesylate over 3 ys

• ( De Matteo RP, Lancet, 2009)

• As a minimum requirements, genotyping should be performed in intermediate-

and high –risk patients as well as in case of neoadjuvant therapy

• Advanced disease:

• Sunitinib malate ( > exon 9 mutations and KIT/PFGRA WT genotype), dasatinib

• Regorafenib

Wada R, Pathol Int, 2016

Gounder M, Cancer Chemother Pharmacol, 2011

Molecular aspects for primary and secondary TKI

resistance in GIST (I)

Primary and secondary resistance to imatinib results in a conformational shift

in the kinase domain of KIT that favors the activated state.

• “Innate”, “Early”, or “primary” resistance are terms to describe patients in whom

progression is noted within 3–6 months of initiating imatinib.

• Early resistance: 20% of all patients.

• Seen with all mutations, but most often with KIT exon 9, PDGFRA, and WT.

• PDGFRA mutations are rare, and definite conclusions regarding response to

imatinib are difficult to make. Exon 12 and 14 are sensitive while D842V PDGFRA

mutations are resistant .

Molecular aspects for primary and secondary TKI

resistance in GIST (II) • “Delayed”, “Acquired”, or “Secondary” resistance :

progression of disease after an initial response or stable disease on imatinib .

Patients develop this resistance between 6 and 24 months of starting therapy

“late” (> 6 months) and “very late” (> 24 months)

• Secondary mutations are found in 50–70% of patients who progress and only in

patients with initial KIT/PDGFRA mutations, especially KIT exon 11.

• T670I “gatekeeper” is the most common secondary mutation. Other mutations are

in exon 14,17, and 18. No secondary mutations have been documented in wild-type

tumors.

• Major mechanisms of imatinib resistance are (1) secondary mutation in KIT or

PDGFRA in addition to the initial mutation, (2) overexpression of KIT as evidenced

by genomic amplification, (3) activation of alternate pathways and loss of KIT, and

(4) functional resistance, defined as mutations in regions of KIT or PDGFR that are

not bound by imatinib.

Model of GIST genomic progression • Most GISTs develop by stepwise accumulation of chromosomal aberrations

• 14q loss in 60-70% of early cases, 22q (50%), 1p (50%) and 15q (40%) in

intermediate and high risk tumors

• Homozygous deletion of tumor suppressor genes

Schafer IM, Nat Commun, 2017

MAX (myc-associated

factor X) inactivation

↓

p16 inactivation and cell

cycle perturbation

Later, inactivating

mutations of p53, RB1

Inactivation of

dystrophin encoded by

DMD gene is a late

event and occurs in

90% of metastatic

GISTs

• GIST : Introduction and History

• Morphology

• Molecular pathology, oncogenesis and prognosis

• Other rare spindle cell tumors of the GI tract and

differential diagnosis

Agenda

Mazur MT & Clark HB,

Am J Surg Pathol, 1983

Perez-Atayde AR

Am J Surg Pathol, 1993

Sarlomo-Rikala M, Mod Pathol, 1998

Hirota S, Science, 1998

Kindblom LG, Am J Pathol, 1998

Milestones