Surgical Pathology Criteria

Squamous Carcinoma of the Anus

Differential Diagnosis

Squamous Carcinoma of the Anus Colorectal Squamous Carcinoma
Must involve anal canal Must not involve the anal squamous mucosa
Some require that colorectal SCC be at least 5-7 cm from the anus

 

Squamous Carcinoma of the Anus Perianal Squamous Carcinoma
Must involve anal canal ≤5 cm from anal verge and entirely visible outside the anal canal on clinical examination
  • Perianal carcinomas have a better prognosis of 85-90% 5 year survival vs. 65-80% for anal squamous carcinomas
  • High risk HPV may be seen in both
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    Squamous Carcinoma of the Anus, Predominantly Basaloid Basal Cell Carcinoma of Perianal Skin
    Involves anal canal Extremely rarely involves anal canal
    May have adjacent squamous carcinoma in situ No relationship to carcinoma in situ
    Frequent necrosis Necrosis infrequent
    BerEp4 and smooth muscle actin negative BerEp4 and smooth muscle actin positive reported up to 100%
    AE1, CK22, CEA, EMA positive 80-100% AE1, CK22, CEA, EMA negative

     

    Squamous Carcinoma of the Anus, Predominantly Basaloid Adenocarcinoma of the Anus, Poorly Differentiated
    CK5/6 and p63 virtually always positive CK5/6 and p63 negative
    CK20 negative CK20 positive if rectal type; negative if perianal gland type
    High risk HPV may be seen in both

     

    Verrucous Carcinoma of the Anus Usual Squamous Carcinoma of the Anus
    Only blunt pushing invasion Jagged invasion
    No more than mild dysplasia Usually significant dysplasia
    Mitotic figures confined to basal layer unless inflamed Mitotic figures may be present at all levels
    No vascular or perineural invasion May have vascular or perineural invasion
    Does not metastasize May metastasize
  • Note that usual squamous carcinoma can develop in verrucous carcinoma
  •  

    Squamous Carcinoma of the Anus Poorly Differentiated Neuroendocrine Carcinoma, Small Cell (Undifferentiated) Type
    CK5/6 and p63 virtually always positive CK5/6 and p63 negative
    CK7 variably positive CK7 negative

     

    Squamous Carcinoma of the Anus Poorly Differentiated Neuroendocrine Carcinoma, Large Cell Type
    CK5/6 and p63 virtually always positive CK5/6 and p63 negative
    At most, scattered neuroendocrine marker positivity Synaptophysin, chromogranin or CD56 extensively positive
    Nests of cells with peripheral palisading At least focal trabeculae, rosettes and/or stippled chromatin

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