Adenocarcinoma of the Colon and Rectum
Definition
- Adenocarcinoma arising in the colon or rectum
Alternate/Historical Names
- For high grade intramucosal neoplasia
- Carcinoma in situ
- High grade dysplasia
- High grade intraepithelial neoplasia
- High grade intramucosal neoplasia
- Intramucosal carcinoma
Covered Separately
- Invasive carcinoma involving an adenomatous polyp
- Adenosquamous colorectal carcinoma
- Hereditary non-polyposis colorectal carcinoma
- Medullary colorectal adenocarcinoma
- Mucinous colorectal adenocarcinoma
- Poorly differentiated endocrine carcinoma
- Signet ring colorectal adenocarcinoma
- Squamous colorectal carcinoma
- Undifferentiated colorectal carcinoma
Diagnostic Criteria
- See Grading/Staging at left for additional critical criteria applicable to problematic situations
- High grade intramucosal neoplasia (high grade dysplasia) requires any one of three criteria below:
- Cribriform architecture
- Back to back gland lumens without intervening stroma
- Should clearly be a manifestation of total loss of polarity by atypical cells
- Frequently, well differentiated mucin producing cells will pile up in adenomas, forming lumens, technically appearing cribriform
- Nuclei show regular basal orientation
- Nuclei typically not markedly enlarged
- This should not be considered evidence of high grade dysplasia
- Severe cytologic atypia
- This is unusual in the absence of cribriform architecture, but can occur
- Invasion with a desmoplastic response confined to the lamina propria including muscularis mucosae
- Invasive adenocarcinoma requires invasion through the muscularis mucosae at least into the submucosa
- Varying degrees of gland formation (see Grading at left)
- Typically lined by tall columnar cells
- Frequent desmoplastic response
- Dirty necrosis commonly seen
- Extensive central necrosis composed of granular eosinophilic karyorrhectic debris
- Frequent surrounding garland of cribriform glands
- Special types of carcinoma are covered separately
- Adenosquamous
- Both glandular and squamous components are malignant
- Medullary
- Pushing border, many intraepithelial lymphocytes
- Mucinous
- >50% composed of mucin
- Poorly differentiated endocrine
- Both small cell and large cell with endocrine differentiation
- Signet ring
- >50% signet ring cells
- Squamous
- Undifferentiated
- 0% gland formation
- The following features are suggestive of microsatellite instability and/or hereditary non-polyposis colorectal carcinoma syndrome (HNPCC) but may also be seen in a subset of sporadic adenocarcinomas
- Intraepithelial lymphocytes, ≥3 per HPF
- Crohn-like response at edge of carcinoma
- Lymphoid aggregates / follicles with or without germinal centers not associated with a lymph node
- Mucinous or signet ring carcinoma component
- Medullary carcinoma
- Less specific criteria
- Right side location
- High grade histology
- Lack of dirty necrosis
- Sporadic carcinomas with these features are frequently MSI high
- Such carcinomas share essentially all histologic features with HNPCC tumors
- May be present in 15% of colorectal adenocarcinomas
- Familial and sporadic cases share some other clinical features
- Better prognosis than non-MSI carcinomas
- Decreased response to 5-FU therapy
- Right sided predominance
- Circumferential / radial margin applies to rectum and non-peritonealized surfaces of colon
- It does not apply to peritoneal surface
- See Grading/Staging for details
- Following features may have prognostic value but have not been sufficiently validated
- Tumor border configuration
- Expansile – smooth and pushing
- Infiltrative
- Limit of carcinoma not definable on naked eye exam of slide
- Inability to resolve carcinoma from host response on naked eye exam of slide
- Streaming dissection / permeation of muscularis propria without desmoplastic response
- Dissection of pericolic fat by single cells, cords or clusters of cells
- Perineural invasion
- Budding
- Based on high power examination of edge of carcinoma
- Detached clusters ≤5 cells each embedded in desmoplastic stroma
- May become spindled (epithelial-mesenchymal transition)
- More often seen in MSI carcinomas associated with HNPCC and with MSS carcinomas but not with sporadic MSI carcinomas
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates: 1/31/10, 7/15/11, 11/12/11
