Mucosal fragments with two of them are ulcerated and heavily infiltrated by a malignant tumor, characterized by a solid, sheet-like, and nested growth pattern infiltrating into the underlying subepithelial stroma, with an absence of distinct glandular formation. The tumor cells exhibit marked cytologic atypia, with active mitosis and foci of tumor necrosis. The surrounding stroma shows desmoplastic reaction with a dense mixed acute and chronic inflammatory cell infiltrate.
Given the anorectal junction location and solid growth pattern, the primary differential diagnosis : poorly differentiated colorectal adenocarcinoma, non-keratinizing anal squamous cell carcinoma, followed by melanoma and less likely large cell neuroendocrine carcinoma and NHL. Recommended for immunohistochemical studies (SATB2, CK20, P63, Synaptophysin, SOX10, CD20, CD3, Ki-67).
Circumferential, friable, and easily bleeding perianal mass extending 5 cm into the rectum.
Soft tissue fragments collectively measured 1 cm, totally embedded.
Anorectal mass, endoscopic biopsy: