Squamous Carcinoma of the Anus
Definition
-
Squamous carcinoma, of varying levels of differentiation, involving the anal canal
Alternate/Historical names
- Basaloid carcinoma
- Basaloid squamous carcinoma
- Cloacogenic carcinoma
- Epidermoid carcinoma
- Mucoepidermoid carcinoma (referring to the mucinous microcystic variant)
- Non-keratinizing squamous carcinoma
- Transitional carcinoma
Covered separately
Diagnostic Criteria
- Must involve the anal canal
- Best determined clinically
- Lesion must not be entirely visible outside the anal canal on clinical examination
- Variable degrees of differentiation and patterns
- Often varies within the same tumor
- Biopsy may not be representative of entire lesion
- Clear squamous differentiation with keratinization and intercellular bridges
- Present to some degree in >90% of cases
- Basaloid, poorly differentiated carcinoma
- Present to some degree in 65% of cases
- Small to moderate amounts of cytoplasm
- Frequent peripheral palisading
- Frequent retraction artifact
- Frequent eosinophilic necrosis in center of nests
- Small cell (anaplastic) carcinoma
- Included by WHO as a variant but not identified in modern studies
- Similar to basaloid pattern (above), but with the following features
- Lack of palisading
- Lack of cohesion
- Diffuse infiltration
- Increased mitotic rate and apoptosis
- In spite of the similar name, this does not refer to small cell (high grade endocrine) carcinoma
- Microcystic (mucoepidermoid) pattern
- Present to some degree in 25% of cases
- Varies from poorly defined to well formed glands
- May contain central stainable mucin
- Prominent basement membrane surrounding and within tumor nodules reminiscent of skin adnexal and salivary gland neoplasms
- Has been given several names
- Cylindroma
- Adenoid cystic carcinoma
- Spiradenocylindroma
- Lacks any myoepithelial layer
- Rare as a dominant pattern
- Has been given several names
- No clear clinical difference has been demonstrated for any of these types and patterns of differentiation or degrees of differentiation with modern therapy
- Diagnosis should simply be Squamous Carcinoma
- Descriptive features may be included in a comment
- Diagnosis should simply be Squamous Carcinoma
- A few studies from the pre-modern therapy era suggested that the mucinous microcystic pattern and the small cell (anaplastic) carcinoma had a worse outcome
- Old version of WHO classification is no longer followed:
- Large cell keratinizing, large cell non-keratinizing and basaloid
- The classification shows poor reproducibility and is not clinically relevant
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/last update : 10/7/10, 3/7/16
