SERRATED PATHWAY TO COLORECTAL NEOPLASIA

~Dr. Pallavi PrasadSenior Resident PathologySGPGIMS, lucknow

Various polyposis including serrated polyposis syndrome

Serrated adenocarcinomas: types, histology and clinical significance

Molecular pathways for different serrated lesions (HPP, SSA, TSA)

Guidelines for management and surveillance of serrated lesions

OUTLINE :

POLYPOSIS SYNDROMES INCLUDING

SERRATED POLYPOSIS AND

DIAGNOSTIC CRITERIA

Familial adenomatous polyposis (FAP)

• 100s-1000s of polyps throughout the bowel. • indistinguishable by either light or electron microscopic

criteria from sporadic adenomatous polyps.• ‘colonic aberrant crypts’, flat adenomas, depressed adenomas

or villous adenomas.• AD• APC gene : chromosome 5q21• germline mutation of the base-excision repair gene MUTYH.

Familial adenomatous polyposis (FAP)

• KRAS mutations -1/4th cases

• other portions of GIT : stomach, small bowel.

• Carcinomas ~ 20 years earlier than the ordinary CRCs (early

30s)

prophylactic colectomy must be performed at 20-25 years of

age

Familial adenomatous polyposis (FAP)

Other GI polyps and malignant lesions:

• Fundic gland polyps in the stomach

• Adenomatous polyps in the stomach and small bowel

• Periampullary carcinoma

• Duodenal cancer

• Congenital hypertrophy of the retinal pigmented epithelium

(CHRPE)

Juvenile polyposis

1 of these three criteria :-

multiple (3-10) juvenile polyps of the colorectum

Any no. of juvenile polyps in a person with a family H/O

juvenile polyposis

Extracolonic juvenile polyposis

• inherited inactivating mutations of SMAD4 or BMPR1A genes.

Peutz Jeghers syndromePJS type polyps Family H/O Characteristic mucocut

pigmentationSTK11 mutation

>=2 histologically confirmed

+ +

+ +

+ +

+

PTEN hamartoma tumor syndrome

• AD

• facial trichilemmomas

• acral keratoses

• oral mucosal papillomas

• colorectal polyps

• increased incidence of malignancy in various sites

• germline mutation in the PTEN gene.

MUTYH associated polyposis

• 1-10 colonic adenomas before 40 yr of age• 10s-100s of colonic adenomas and/or hyperplastic polyps• Colonic polyposis (i.e. > 100 colonic polyps) in the absence of

a germline APC mutation• Colorectal cancer with the somatic KRAS mutation• Family H/O colon cancer (with or without polyps) consistent

with autosomal recessive inheritance

• Biallelic MUTYH mutation

Lynch Syndrome

• onset of colorectal cancer at an early age (~45 yr)• proximal (right sided) colon cancer• High r/o multiple primary colorectal tumors (synchronous or

metachronous)• Specific pathological features of lynch syndrome: Poorly differentiated Mucinous Signet cell features Crohn’s like lymphocytic reaction Excess of tumor infiltrating lymphocytes

Lynch Syndrome

• Increased risk of cancer at extracolonic sites:

endometriumPancreas,

hepatobiliary tract

ovary

Brain (turcot’s syndrome)

Stomach, small bower

Upper urothelial tract

Sebaceous adenomas, Ca,

keratoacanthomas

Lynch Syndrome • hereditary non-polyposis colorectal cancer syndrome• AD• germline mutation in DNA mismatch repair gene (MSH2,

MLH1, MSH6, and PSM2) “first hit,” • Inactivation of the remaining normal allele “second hit.” • loss of mismatch repair function & accumulation of mutations

in repeated DNA sequences (microsatellites)

increased susceptibility to accumulate mutations in genes

with microsatellite regions

Process of DNA mismatch repair

Lynch Syndrome

• Two of the MMR genes, MSH3 and MSH6, themselves contain

coding microsatellites that can be mutated in MSI-high (MSI-

H) cancers : mutational targets.

• BRAF gene is almost never mutated in Lynch syndrome–

associated CRCs.

Serrated Polyposis Syndrome

= hyperplastic polyposis syndrome

• Multiple, small, sessile polyps, throughout the colorectum

• Variable in histological appearance, even within the same

patient (majority SSA/Ps and MVHPs).• M=F; 42- 66 years

• 2 clinical subtypes : • Type1 : multiple, more proximal, larger SSA/Ps (carcinoma)• Type 2: numerous small HPs, throughout the colon.

Criteria for the diagnosis of serrated polyposis (‘hyperplastic polyposis’)

At least five histologically diagnosed serrated polyps proximal

to the sigmoid colon (two are >10 mm in dia) or,

Any number of serrated polyps occurring proximal to the

sigmoid colon in an individual who has a 1st degree relative

with serrated polyposis or,

>20 hyperplastic polyps of any size but distributed throughout

the colon

Serrated Polyposis Syndrome

• Increased risk of carcinoma (x5.4)

• Screening age :

>40 yrs

10 yrs younger than the age of diagnosis of youngest relative

SERRATED PATHWAY CARCINOMAS

• The “serrated neoplastic pathway” describes the progression

of serrated polyps, including SSAs and TSAs to colorectal

cancer.

• These findings are particularly relevant to prevention of

interval cancers through colonoscopy surveillance programs

—an important issue for colonoscopists.

Proximal colon-missed by colonoscopy

Flat/sessile morphology

Ill-defined borders of SSAs

Rapid growth of MSI cancers

Interval colon cancer

(2.9-7.9%)

Serrated pathway carcinomas

• Diverse range of histological appearances, molecular profiles

and biological behaviours.

• Share serrated pathway histogenesis..

• Most arise in distal colon or rectum

• MSI-H or MSI-L

• Worse prognosis than CRC developing along the ‘adenoma

carcinoma’ pathway• Tumour budding, infiltrative growth pattern and lymphatic

invasion

Serrated pathway carcinomas

• > in women

• m/c : caecum or ascending colon > rectum

Three major histological patterns:

well to moderately differentiated adenocarcinoma with

serrated morphology

mucinous adenocarcinoma

trabecular

Serrated pathway carcinomas

Histological criteria of serrated morphology carcinomas

Epithelial serrations Eosinophilic or clear cytoplasm Abundant cytoplasm Vesicular nuclei with peripheral chromatin condensation &

single prominent nucleolus Distinct nucleoli Absence of necrosis (or <10% necrosis) Intracellular and extracellular mucin Cell balls and papillary rods*

Well-differentiated adenocarcinoma

mucinous

trabecular

BRAF mut tumours : located mainly proximally, CIMP-H and

either MSI or MSS

KRAS mut tumours : distal, CIMP-L , MSS.

• Mucus production, with high levels of expression of MUC2,

MUC5B, MUC5AC and MUC6

• poor differentiation

• tumour-infiltrating lymphocytes

• Crohn’s-like peritumoral lymphocytic response

Serrated pathway carcinomas

• The most reliable histological marker of serrated pathway

histogenesis is the finding of a contiguous residual serrated

polyp, SSA or TSA.

Serrated pathway carcinomas

MOLECULAR PATHWAYS FOR DIFFERENT SERRATED LESIONS

Genetic Alterations In Serrated Lesions And Progression To Cancer

Adenoma-carcinoma sequence

APC

KRAS

p53

SMAD4

Serrated pathways

BRAF

KRAS

h-MLH-I

p16

MGMT

• BRAF : (proto-oncogene) B-Raf (Raf kinase family of

phosphorylating enzyme) cell division and

differentiation.

• Malignant melanoma and carcinomas of the lung and

colorectum.

• > 30 mutations recognised in the BRAF gene.

• V600E mutation = most common (90% of BRAF mutations).

valine (V) to glutamate (E)

BRAF

• in cancer cells with MSI and in serrated polyps

• A single, activating, point mutation in BRAF (V600E)

KRAS

constitutive signaling of the mitogen-activated protein kinase

(MAPK) pathway

cell proliferation, survival, inhibition of apoptosis

• never in conventional adenomas and HNPCC.

• BRAF mutation correlates with CIMP.

• most SSAs (75%–83%) have a BRAF mutation + CIMP-H

• mutated very early in the serrated pathway, in 70%–76%

MVHP, pts with HPS.

• in serrated hyperplastic aberrant crypt foci - earliest

histologically evident lesions in the serrated pathway.

BRAF

• p16 : encodes cyclin-dependent kinase inhibitor 2A cell

cycle control.

• mutated in several different cancers.

• MGMT : encodes the MGMT protein (methyl guanine

methyltransferase)

hypermethylation of promoter sequence

DNA repair

• KRAS :

• KRAS protein (proto-oncogene) Ras family of proteins

signalling in normal cells.

• In carcinomas of the pancreas, lung, colorectum.

• In CRC, KRAS mutation : predictor of a poor response to EGFR

inhibitors such as cetuximab .

CIMP

Epigenetic phenomenon

Generally all MSI-H cancers CIMP high

CIMP• > a/w BRAF mutation

• >1cm polyps with high grade dysplasia

• Corelates with MSI status

• in serrated polyps from patients with HPS, supporting the

importance of CIMP in the serrated pathway.

• also in serrated polyps (proximal SSA)

• Yang et al detected CIMP, in order of increasing frequency :

MVHP (47%) < SSA (75%) < TSA (80%)

CIMP• Methylation of CIMP loci was even detected in histologically

normal colorectal mucosa of HPS patients (Worthley et al) .

• Together these data indicate that although the cellular

methylation machinery might be disrupted at early stages of

tumorigenesis, concurrent, high-level methylation of specific

CIMP loci facilitates the transition from MVHP to SSA.

MSI

• a hallmark of colorectal cancer arising in the context of

Hereditary Non Polyposis Colorectal Cancer (HNPCC) or Lynch

syndrome

loss of mismatch repair genes(MMR)

increased susceptibility to accumulate mutations in genes

with microsatellite regions

MSI • microsatellite : tract of repetitive DNA in which certain DNA

motifs (ranging in length from 2–5 base pairs) are repeated,

typically 5-50 times.

• occur at thousands of locations in the human genome.

• high mutation rate and high diversity in the population.

• in non-coding DNA : biologically silent

• In regulatory or coding DNA : phenotypic changes and diseases.

MSI• panel of 5 microsatellites sequencing [Bethesda panel] :

• two mononucleotide markers (BAT 25 and BAT 26)

• three dinucleotide microsatellites (D5S346, D2S123 and

D17S250)MSI-H (high MSI)

• >=2 unstable markers

MSI-L (low MSI)

• 1 unstable marker

MSS(Microsatellite stable)

• No unstable marker

MSI

• Presence of mutations in genes with microsatellite region =

MSI target genes.

• MSIH tumors exhibited a distinct genetic pathway of the MSS

and MSIL tumors.

• Stefanius et al : 20.6% of serrated cancers showed MSI-H.

Diagram representing the main pathways and molecularalterations of sessile serrated neoplasia, conventional adenomatouspathway, and alternative pathway.

Molecular pathways underlying various hyperplastic

polyps

EGFR

BRAF mutation occur early in the development of hyperplastic aberrant crypt foci.

BRAF corelates strongly with CIMP-H phenotype.

MVHPs and SSA/Ps have nearly overlapping molecular patterns (CIMP, KRAS, BRAF)..

Molecular pathways underlying

Sessile serrated adenomas/polyps (SSA/SSAPs)

DNA mismatch repair proteins are

intact in all cases.

Role of MGMT.

Molecular pathways underlying

traditional serrated adenomas

(TSAs)

•

GUIDELINES FOR MANAGEMENT AND SURVEILLANCE OF SERRATED

POLYPS

• low-risk adenomas (<3 tubular adenomas, < 10 mm in

diameter, low-grade dysplasia only)-surveyed at 5- to 10-year

interval

• high-risk adenomas (>=3 adenomas, size >10 mm or larger,

high-grade dysplasia, significant villous histology) are

surveyed at 3-year intervals

Arch Pathol Lab Med.2015;139:730-741. Molecular and Histologic ConsiderationsIn the Assesment of Serrated Polyps

US Multi society task force (2012)

Key messages

• ‘Serrated neoplasia’ refers to a range of colorectal lesions with

varying degrees of malignant risk, together with distinct forms

of adenocarcinoma.

• Bowel Cancer Screening Programmes have highlighted to

histopathologists the importance of recognizing and

understanding the biological significance of the spectrum of

serrated lesions.

• The optimal terminology, minimum diagnostic criteria and

most appropriate management strategies for some serrated

lesions (especially the sessile serrated lesion) are still in

evolution.

Key messages

Further reading :

• Arch Pathol Lab Med.2015;139:730-741. Molecular and

Histologic Considerations in the Assesment of Serrated Polyps.

• J Clin Pathol 2014;67:865–874. Bateman AC. Pathology of

serrated colorectal lesions.

• World J Gastroenterol 2014 March 14; 20(10): 2634-2640.

Serrated pathway in colorectal carcinogenesis.

• Histopathology 2015;66, 49–65.Colorectal serrated pathway

cancers and precursors.

• American journal of gastroenterology 2009;13 Role of

serrated pathway in colorectal cancer pathogenesis.

8(6):2088-2100.

• Journal of colon and rectal cancer 2013;1(1). Serrated lesions

of colorectum: A new pathway in colorectal carcinogenesis.

• Gastroenterology 2010;138:2088–2100. Role of the Serrated

Pathway in Colorectal Cancer Pathogenesis

• Histopathology 2013, 62, 367–386. The serrated pathway to

colorectal carcinoma: current concepts and challenges.

• American Journal of Clinical Pathology 2012,137,847-859.

Molecular Testing in Colorectal Cancer

THANK YOU