Colorectal Adenocarcinoma

 

Common sites:

    • 55% are in rectosigmoid colon
    • MSI pathway carcinomas:
      • Proximal (right) colon

 

Gross features:

    • R colon cancers tend to be polypoid, exophytic masses
    • L colon cancers tend to be annular, constrictive lesions.
    • Completeness of mesorectum (rectal carcinomas)
      • Predictive of local recurrence
      • Incomplete:
        • Little bulk to mesorectum
        • Defects of mesorectum down to muscularis propria
        • Irregular circumferential margin  after transverse sectioning
      • Nearly complete:
        • Moderate bulk to mesorectum
        • Irregularity to mesorectum with defects > 5 mm (none extending to muscularis propria)
        • Only the insertion site of levator ani muscles is visible muscularis propria
      • Complete:
        • Intact bulky mesorectum with a smooth surface
        • Only minor irregularities
        • No surface defects > 5 mm
        • No coning towards distal margin of specimen
        • Circumferential margin appears smooth after transverse sectioning

 

Histologic features:

    • Cribriform arrangement of glands
    • Invasion, which is accompanied by a strong desmoplastic response
    • Low-grade:
      • Well-differentiated – more than 95% glandular architecture
      • Mod-differentiated – more than 50% glandular architecture
    • High-grade:
      • Poorly-differentiated – less than 50% gland architecture
      • Undifferentiated – less than 5% gland architecture
    • Mucinous subtype
      • more than 50% showing stromal mucin
        • If mucinous areas are < 50% it is categorized as having a mucinous component
      • Many are MSI-H
      • Behaves as high-grade carcinoma if it is MSS or MSI-L (not MSI-H)
    • Signet ring carcinoma
      • > 50% signet ring cells
        • < 50% is termed “with a signet-ring cell component”
      • Poor prognosis (if it lacks MSI-H)
    • Medullary Carcinoma (favourable prognosis)
      • Sheets of malignant cells
      • Vesicular nuclei
        • Prominent nucleoli
      • Abundant eosinophilic cytoplasm
      • Rare
      • Almost invariably MSI-H
    • Serrated adenocarcinoma
      • Rare
      • Sessile serrated polyp type architecture
        • Glandular serration
        • Mucinous, cribriform, lacy, and trabecular areas maybe
        • Low N:C ratio
      • MSI-L or MSI-H maybe
      • BRAF mutations maybe
      • CpG island hypermethylation maybe
    • Cribriform comedo-type adenocarcinoma:
      • Rare
      • Extensive large cribriform glands with central necrosis
        • Analogous to breast adenocarcinomas
      • Usually MSS with CpG island hypermethylation
    • Micropapillary adenocarcinoma
      • Rare
      • Small clusters of tumour cells within stromal spaces mimicking vascular channels
        • Same as described in breast and bladder cancer
      • May be seen as a component in a conventional CRC
      • Characteristic MUC1 staining pattern by IHC
    • Adenosquamous carcinoma
      • Either separate areas within the tumour, or admixed
      • More than just occasional small foci of squamous differentiation
      • Pure squamous cell carcinoma is very rare
    • Spindle cell carcinoma
      • Biphasic with a spindle cell sarcomatoid component
      • Spindle component is at least focally IHC+ for keratins
    • Undifferentiated carcinoma:
      • Rare
      • Lacking morphological, immunohistochemical, and molecular biological evidence of differentiation beyond that of an epithelial tumour
      • Variable histologic features
      • Some have MSI-H
    • Small cell carcinoma
      • Poor prognosis
    • Clue for metastases:
      • Necrotic debris rimmed by a row of malignant cells
    • MSI carcinomas:
      • Some hyperplastic polyps and many sessile serrated adenomas show this pathway of carcinogenesis
      • Medullary growth pattern
        • Solid
        • Nested
        • Organoid
        • trabecular
      • Mucinous or signet ring cell differentiation
      • Prominent lymphocytic response to tumour
        • Tumour infiltrating lymphocytes ( >= 3 / HPF)
        • Crohn-like extratumoural lymphoid follicles
      • Negative for immunohistochemical neuroendocrine differentiation
      • Lack of dirty necrosis
    • Malignant Polyps (polyps with invasive adenoCA)
      • Invasion through the muscularis mucosa into the submucosa (pT1)
        • (Invasion within lamina propria or MM is reported as HGD)
      • Report the following for malignant polyps (may require colectomy with lymph node examination):
        • Poorly differentiated component (presence or absence, any amount)
        • LVI (presence or absence)
        • Distance to margin (1mm or less is considered positive) (some do not agree with this criterium)
      • Optional reporting elements:
        • Tumour budding (not widely accepted)
        • Haggitt level in pedunculated polyps
        • Sessile polyp with invasion below the background muscularis mucosa (not widely accepted)
    • Tumor budding (poor prognosis, but no uniformly accepted criteria currently):
      • Criteria of Ueno et al for ‘high-grade budding’
        • >= 10 groups of < 5 cells in a 20x objective field
        • IHC may be used for cases with 5-10 definite buds and some indefinite, but should not be used routinely
        • Concentrate on invasive tumour front

 

Immunophenotype:

Marker:

Sensitivity:

Specificity:

CEA

 

 

CK7 (–)

 

 

CK20 (+)

Some are CK20-

(tend to be MSI-H) 

 

CDX-2

Most

(not associated with MSI status)

 

MLH1

Negative in some MSI carcinomas

(sporadic or HNPCC)

 

MSH2

Negative in some MSI carcinomas (HNPCC)

 

MSH6

Negative in some MSI carcinomas (HNPCC)

 

PMS2

Negative in some MSI carcinomas (HNPCC)

 

 

 

Molecular features:

    • Sporadic:
      • Chromosomal instability pathway (~75%):
        • APC mutation (> 90%)
          • Biallelic APC mutation (early in development of conventional adenomas)
          • APC normally facilitates the sequestration and degradation of cytoplasmic beta-catenin, thereby regulating cell proliferation
          • also regulates microtubule function
            • dysfunctional APC results in abnormal chromosomal segregation during mitosis
            • genetic instability
            • LOH
        • Wnt signaling pathway abnormalities
        • KRAS mutation (50%) (prognostic effect is controversial)
          • [Draft recommendation] : RAS mutation testing should be performed for patients who are being considered for anti-EGFR therapy.
            • Must include KRAS and NRAS codons 12 and 13 of exon 2; 59 and 61 of exon 3; and 117 and 146 of exon 4 (« expanded » or « extended » RAS)
          • 20% of KRAS exon 2 non-mutated tumours harboured one of the extended RAS mutations
          • [Draft expert consensus opinion] :
            • Labs should use molecular marker testing methods that are able to detect mutations in specimens with at least 5% mutant allele freqeuncy, taking into account the analytical sensitivity of the assay (level of dection / LOD) and tumour enrichment (ex. microdissection).  It is recommended that the operational minimal neoplastic carcinoma cell content tested should be set at least 2 times the assay’s LOD.
        • BRAF mutation (?poor prognosis)
          • Mutually exclusive with KRAS
          • [Draft recommendation ] : BRAF V600 mutational analysis in conjunction with dMMR/MSI testing must be performed in carcinoma tissue of patients with metastatic colorectal carcinoma for prognostic stratification
          • [Draft no recommendation] : There is insufficient evidence to recommend BRAF V600 mutational status as a predictive molecular marker for response to anti-EGFR inhibitors (53% agree, 16% disagree)
        • PIK3CA mutation (25%) (late event) (?poor prognosis)
          • [Draft no recommendation] : There is insufficient evidence to recommend PIK3CA mutational analysis for therapy selection outside of a clinical trial.
        • TP53 mutation (70%)
        • PTEN loss :
          • [Draft no recommendation ] : There is insufficient evidence to recommend PTEN analysis (IHC or FISH) for patients being considered for therapy selection outside of a clinical trial.
        • FBXW7/CDC4 mutation (late event)
          • ?related to aneuploidy
        • CHEK2 mutation (low frequency)
        • BUB1 mutation (low frequency)
        • Aneuploidy and structurally unbalanced rearrrangements
          • Increased nuclear DNA content
        • Losses :
          • 18q loss (?poor prognosis)
          • Loss of SMADs
          • Loss of p53
      • Microsatellite instability pathway / serrated neoplastic pathway (15% of sporadic, nearly 100% in HNPCC):
        • Microsatelite instability caused by hypermethylationof cytosine residues at CpG islands within promoter region of MLH-1, MSH-2, MSH-6, MSH-3, PMS-2, or TACSTD1) (sporadic)
          • MLH-1 mostly
          • Usually associated with loss of expression of the protein but not always
          • This can be evaluated by looking at 5 loci by PCR (compare to non-tumour tissues in same patient)
            • low-frequency (MSI-L) – 1 locus with allelic shift (often grouped with MSI-stable tumours)
            • high-frequency (MSI-H) – 2 or more loci with allelic shift
            • microsatellite –stable (MSS) – 0 loci with allelic shift
        • CpG island methylator phenotype (CIMP)
        • Loss of O6-methylguanine-methyltransferase (MGMT expression
        • Mutations:
          • BRAF mutations (50%) (present in sporadic MSI but not Lynch syndrome)
          • APC mutation
          • RARELY:
            • KRAS
          • Frequent frameshift mutations:
            • TGFBR2
            • IGF2R
            • BAX
            • TCF7L2
            • E2F4
            • PTEN
            • MSH6
            • MSH3
            • CASP5
            • BMPR2
          • Lynch Syndrome-associated:
            • CTNNB1 mutation (alternative to APC)
            •  
        • diploid usually
        • LOH frequency is low, including 5q
        • Associated clinicopathologic characteristics:
          • Right-sided
          • Mucinous
          • Medullary (occasionally)
          • Crohn-like peritumoral lymphocyte infiltrate
          • Intratumoural lymphocyte infiltrate
          • Devoid of “dirty” necrosis
          • Lower stage
          • Expansile growth
          • Better stage-specific prognosis
          • less responsive to certain chemotherapies (5-FU and oxaliplatin)
          • better response to irinotecan maybe
      • microsatellite-stable and chromosome-stable tumours (up to 15%)
        • not well studied
      • CpG island methylator phenotype (CIMP) tumours:
        • Widespread CpG island methylation (type C methylation)
        • Often MSI-H but > 50% are microsatellite stable
        • KRAS mutation and microsatellite stable (CIMP2)
        • BRAF mutation with MSI-H (CIMP1)
        • TP53 mutation and microsatellite stable (CIMP-negative

o   MSI (PCR) testing (93% sensitivity for identifying individuals with a germline MMR gene variant – Shia 2008) (range of 75-100% - CCO evidence review)

§  Test tumour tissue and normal tissue concurrently

§  Panel of 5 microsatellite markers (recommended BAT25, BAT26, D2S123, D5S346, and D17S250)

·       MSI-high: > 30 % of markers show instability

·       MSI-low: < 30% of markers show instability

·       MSI-stable: 0% of markers show instability

    • Familial:
      • FAP
      • Hereditary non-polyposis colon cancer – HNPCC
        • germline mutation of one of mismatch repair genes (MLH-1, MSH-2, MSH-6, MSH-3, PMS-2)

 

Other features:

    • histologic type can be prognostic (see above)
    • perforation at tumour is associated with poor prognosis
      • Perforation proximal to tumour also has a high mortality
    • Treatment response pathologically is prognostically significant
      • Minimal residual disease is better than gross residual disease
      • Acellular pools of mucin don’t count as residual disease
    • MMR deficient (MMR-D) / MSI positive sporadic cancers:
      • Better prognosis
        • Lower recurrence risk in stage II and III
      • Limited benefit from 5-FU-based chemotherapy in stage II
    • Mutations conferring resistance to anti-EGFR monoclonal antibodies cetuximab and panitumumab:
      • KRAS (note: G13D appears to be an exception)
      • ?BRAF
      • ?PIK3CA
      • PTEN loss of expression
    • EGFR amplification may predict favourable response to EGFR inhibitors

 

References:

    •  Robbins 2007
    • WHO Classification of Tumours of the Digestive System (2010)
    • EGAPP Working Group, Genetics in Medicine, 2013, PMID:23429431
    • Mitrovic B, Schaeffer DF, Riddell RH, Kirsch R.  Tumor budding in colorectal carcinoma: time to take notice.  Modern Pathology (2012) 25:1315-1325.
    • National Colorectal Cancer Screening Network Classification of Benign Polyps: Pathology Working Group Report (June 2011)\
    • [Draft ASCP/CAP/AMP/ASCO Guideline on the Evaluation of Molecular Markers for Colorectal Cancer] – March 2016