5,070 new cases in 2008 with increasing incidence over the last three decades. Majority are SCC (75–80%); others are adenocarcinoma or melanoma. HPV: strongly associated with SCC and may be requisite for disease formation. High-grade intraepithelial lesions are precursors. In particular HPV-16, 18 as in cervical cancer. AIDS is associated with anal cancer, likely through an association with immunodeficiency in the setting of HPV coinfection. Increased risk if CD4 < 200. Additional Risk Factors: > 10 sexual partners, history of anal warts, history of anal intercourse < age 30 or with multiple partners, history of STDs. Anatomy: anal canal is 3–4 cm long. Extends from anal verge to the anorectal ring. The dentate line lies within the anal canal and divides it by histology. Proximal to the dentate line is colorectal mucosa, distal to it is nonkeratinizing squamous epithelium. The dentate line contains transitional mucosa. Anal margin is 5 cm ring of skin around the anus. Use CT to measure depth of inguinal nodes using the femoral vessels as a surrogate: large variations exist (Koh et al. 1993). Anal margin tumors: may behave like skin cancers, and can be treated as skin cancer as long as there is no involvement of the anal sphincter, tumor < 2 cm, moderately or well-differentiated. Adenocarcinoma: higher local and distant recurrence rates with chemo-RT compared to SCC. Use 5-FU chemo-RT pre-op followed by APR (Papagikos et al. 2003). Lymph node drainage: superiorly (above dentate line) along hemorrhoidal vessels to perirectal and internal iliac nodes; inferior canal (below dentate line) and anal verge to inguinal nodes. Presentation: bleeding, anal discomfort, pruritis, rectal urgency.
KeywordsAnal Canal Anal Verge Anal Cancer Inguinal Node Dentate Line
We thank Richard M. Krieg for his valuable advice in the preparation of this chapter.
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