Adenocarcinoma of the Anus

Differential Diagnosis

Colorectal Type Adenocarcinoma of the Anus	Extra-mucosal (Fistula/Anal Gland) Type Adenocarcinoma of the Anus
Usually has identifiable surface component	No surface mucosal component
No association with chronic fistula	Most case associated with chronic fistula
CK7 variably positive	CK7 positive
CK20 positive	CK20 negative
CDX2 positive	CDX2 negative

Small numbers of cases have been tested

Squamous Carcinoma of the Anus	Poorly Differentiated Adenocarcinoma of the Anus
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

Melanoma should be ruled out before the diagnosis of poorly differentiated adenocarcinoma is made