Other risk factors include an increasing number of sexual partners, a history of anogenital warts,8 previous lower genital tract dysplasia or carcinoma, and a history of smoking.15 In addition to HIV infection, immunosuppression in solid organ transplant16 and immune disorders have also been shown to be risk factors.

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The anatomy of the anal canal is important in understanding SCC of the anus. There are three distinct entities of the anus, namely the rectum, anus, and anal margin. The surgical anal canal (Fig. 1) extends cephalocaudally from the level of the pelvic floor (the anorectal ring or the junction of the puborectalis portion of the levator ani muscle with the external anal sphincter) to the proximal margin of the anal verge.

Thus defined, the anal canal corresponds to the segment that is invested by the internal anal sphincter and is about 4.0 cm in length. The dentate (pectinate) line is located approximately two-thirds of the distance proximally from the anal margin. Tumors involving the anorectal junction should be classified as rectal cancers if the epicenter is 2 cm or more proximal to the dentate line (Fig. 2).


The blood supply comprises branches of the superior rectal artery, the inferior rectal branch of the pudendal artery, and branches of the median sacral artery. The venous drainage is divided into two, whereby above the dentate line, the terminal branches of the superior rectal vein drain into the inferior mesenteric vein and portal system, and below the dentate line, they drain via the inferior rectal vein into the pudendal vein, passing to the internal iliac vein.17

The lymphatic drainage of the anal canal is dependent primarily on the location of the tumor in relation to the dentate line. In the normal, ie, non-HIV population, squamous cell cancers extending above the dentate line are relatively rare. Hence, SCC of the rectum is not a common entity.

Below the dentate line, drainage to the inguinal and femoral nodes occurs, while above the dentate line, there is drainage to the perirectal and paravertebral lymph nodes. Therefore, proximal anal cancers located in the anal canal may drain to the lymph nodes along the inferior mesenteric artery. Meanwhile, distal anal canal and anal margin lesions will metastasize to the inguinal lymph nodes.17,18

Clinical Presentation

Symptoms of AIN are similar to common benign anorectal diseases, and therefore, all patients should be properly assessed to avoid delays in diagnosis. The following signs and symptoms are common in anal cancers:

Bleeding: Bleeding from the anal area occurs in more than half of the patients with anal cancer, and it is usually the first sign of the disease.

Mass: Patients may present with a perianal swelling which may be wart-like or ulcerative.

Pruritis: Itching around the anus is more common in people with AIN than anal cancer. However, pruritis ani can be a symptom of anal cancer.

Pain: About one-third of people with anal cancer feel pain. This may be post-defecation as with an anal fissure or due to invasion into the anoderm and the sphincter complex.

Change in bowel habit: Patients may experience tenesmus or, if there is sphincter involvement, patients may develop incontinence.

Localized inguinal lymphadenopathy: A localized inguinal lymphadenopathy may also be present with symptoms of metastatic disease.3,4,6