Anal margin neoplasms have a low-grade malignant potential and are slow to metastasize. Anal canal neoplasms, on the other hand, are far more virulent, metastasize early, and have a poor prognosis. Squamous cell carcinoma of the anal canal has a much poorer prognosis than its anal margin counterpart. Anal canal malignancies metastasize not only to mesenteric lymph nodes and the portal circulation but also to the regional inguinal nodes and via the systemic circulation.
Included among the anal canal neoplasms is Kaposi's sarcoma, the most common AIDS-related malignancy. Ihe anal canal is the third most common site for malignant melanoma (after the skin and the eye), which, when it occurs there, may not be pigmented and is frequently overlooked.
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