Anal cancer is a type of cancer that affects the anus. The anus is a region in the gastrointestinal tract that is located at the end of the colon and below the rectum. It functions as an opening for stool or waste to pass out the body.

A tumor can potentially develop anywhere. This happens when the rate of cell growth is faster than normal leading to abnormal cell development. When enough of these cells reproduce, a benign or a malignant tumor can form. Benign tumors are non-cancerous growths, while malignant tumors are harmful and can spread to other areas of the body. Abnormal cell masses in the early phases are referred to as dysplasia. Dysplasia in the anus is called anal epithelial neoplasia (AIN). Noncancerous growths can also occur in and outside of the anus, which includes warts and polyps.

Different types of anal cancer can form depending on where cancer began developing. Squamous cell carcinoma is the most common type and forms at the outer lining of the anal canal. Cloacogenic carcinoma makes up around 25% of all anal cancer cases. A few other types of anal cancer include adenocarcinoma, basal cell carcinoma, and melanoma.

Risk Factors

A common risk factor found in most squamous cell anal cancer patients is the human papillomavirus (HPV). HPV is a virus that causes genital and anal warts. It is usually transmitted from one person to another through skin-to-skin contact like sexual activity. There are many types of HPV subtypes, but genital and anal warts are commonly linked to HPV-6 and HPV-11. These warts alone usually do not lead to cancer. However, other strains of HPV are frequently associated with anal cancer. Other risk factors can include HIV and smoking. For women, in particular, having been diagnosed with vulva, cervix, or vaginal cancer can increase the risk of anal cancer.

Tests for Anal CancerThere are several screening methods used to diagnose anal cancer. Endoscopic procedures can be used to gain a visual of the inner walls of the anal canal to assess for any abnormal growth. Biopsies or brushings are also performed to get tissue samples from endoscopic exams for pathological analysis.

Some exams, such as an anal pap smear for screening abnormalities in the anus, can be performed in the office. During an anoscopy, a short and hollow tube called an anoscope is inserted into the anus and the rectum. A light is projected inside the tube to provide a visual of the lower rectum and anus.

Other diagnostic tools include imaging tests like endoscopic ultrasounds, MRIs, CT scans, and colonoscopy. CT scans are helpful for assessing the cancer’s progress or spread to other organs. MRI imaging is sometimes used to check for irregularities in the lymph nodes. Changes in size can indicate that the cancer has spread.


Author Leo Treyzon MD

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