The most common type is squamous cell carcinoma.
Associated with HPV infection and common in men who have sex with men and in immunosuppressed patients, especially those who are HIV positive.
Presenting symptoms are typically bleeding and anal pain.
The cure rate is high (75% to 90%).
Most patients are cured without a colostomy.
Standard treatment for anal cancer is fluorouracil/mitomycin plus radiation therapy.
More intensive chemotherapy and radiation has not improved results.
Cancers of the anus can occur in 3 regions: the perianal skin, the anal canal, and the lower rectum. In most patients, the anal canal is 3 to 4 cm long and extends from the anal verge to the pelvic floor. A clear anatomic distinction between the anal canal and the anal margin is needed because of the different natural histories of cancers that arise in these 2 areas. There is considerable confusion when comparing series in the literature because of the different definitions used for the anal canal and the anal margin.
To clarify this issue, the American Joint Committee on Cancer (AJCC) and the Union Internationale Contre le Cancer (UICC) agreed that the anal canal extends from the anorectal ring to the anal verge. This is an important distinction because these 2 governing bodies also agreed that anal margin tumors behave in a similar fashion to skin cancers and should be classified as skin tumors and treated as such. However, if there is any involvement of the anal verge by tumor, it should be treated as an anal canal cancer.
There is a variety of histologic cell types in the anal area.
[1]
Peters RK, Mack TM. Patterns of anal carcinoma by gender and marital status in Los Angeles County. Br J Cancer. 1983;48:629-636.
http://www.ncbi.nlm.nih.gov/pubmed/6639856?tool=bestpractice.com
The most common malignancy is squamous cell carcinoma. Because the mucosal epithelium over the rectal columns is cuboidal, transitional or cloacogenic carcinomas can arise. Most investigators agree that prognosis is more dependent on stage than histologic subtype. In contrast, a study using a multivariate analysis has reported a higher distant metastasis rate for patients with basaloid histologies.
[2]
Das P, Bhatia S, Eng C, et al. Predictors and patterns of recurrence after definitive chemoradiation for anal cancer. Int J Radiat Oncol Biol Phys. 2007;68:794-800.
http://www.ncbi.nlm.nih.gov/pubmed/17379452?tool=bestpractice.com
Adenocarcinomas can arise from anal crypts and should be treated as a rectal cancer. Because of their location and their higher lymphatic flow compared with rectal adenocarcinomas, anal crypt adenocarcinomas have a higher risk of inguinal node spread. Squamous cell and cloacogenic histologies are collectively defined as anal canal cancers. Other rare histologic entities can arise, such as small cell neuroendocrine carcinomas, lymphomas, and melanomas.