THE malignancies of the anal canal, which comprise less than 5% of the malignancies involving the colon and rectum, are almost always keratinizing squamous cell epidermoid cancers. The squamous cell lesions are distinguished by epithelial pearl keratin formations. However, occasionally a nonkeratinizing cancer appears in the anal canal or perianal region and, because of its rarity, it is often overlooked in differential diagnosis. The various tumors arise from specific zones of origin in the anal canal.
Five types of nonkeratininizing cancers have been seen in the anal region. These nonkeratinizing anal malignancies show wide variations in cellular pattern and in dynamics of growth. Two of them, the basal cell carcinoma and perianal Bowen's disease, have a low invasive potential and, if recognized early, can easily be eradicated by local excision. The malignant melanoma of the anal canal, however, offers an almost hopeless prognosis even after the most radical surgery. The
GRODSKY L. Rare Nonkeratinizing Malignancies of Anal RegionPathologic Features. Arch Surg. 1965;90(2):216-221. doi:10.1001/archsurg.1965.01320080040009