Anal cancer refers to a variety of cancers that occur in and around the anus or anal canal. While largely uncommon and treatable, anal cancer is on the rise. The average age of onset is the early 60s, and the disease seems to affect women more than men.
Different types of cancer are found in various parts of the anal canal. Most anal cancers found in the U.S. are squamous cell carcinomas, tumors that originate in the squamous cells that line the anal margin and most of the canal. Some anal cancers, called adenocarcinomas, arise from the rectum and are treated like rectal cancer. Although instances are infrequent, Basal cell carcinomas – and even malignant melanomas – can also be types of anal cancer. Those cancers are much more common in parts of the body that are exposed to the sun.
The anus is also prone to benign tumors, including polyps and other growths; pre-cancerous conditions, most commonly in the form of condylomas, or warts. Anal warts are caused by infection with the human papilloma virus (HPV), which also causes cervical cancer. Sometimes changes can occur in the cell lining of the anal canal, leading to dysplasia, or anal intraepithelial neoplasia (AIN). Low grade AIN is generally harmless and resolves itself without treatment, while high-grade AIN can develop into cancer and needs to be watched, if not treated.
Being infected with HPV is a risk factor for anal cancer. Other risk factors include having anal intercourse, smoking, having a suppressed immune system, and being infected with the human immunodeficiency virus (HIV). For men, being uncircumcised and having multiple sexual partners can lead to both HPV and anal cancer. Women's risk of anal cancer increases if they have ever had cancer of the cervix, vagina, or vulva; became sexually active at a young age; have multiple sex partners; or have intercourse with uncircumcised men.
Anal cancer often does not produce any symptoms. However, about half the cases will exhibit some of the following: rectal bleeding, itching, pain, swelling, abnormal discharge, or changes in stool size. Fortunately many anal cancers can be detected early, through a digital rectal exam performed at a yearly checkup.
People who have some or all of the risk factors or who are diagnosed with AIN may consider anal cytology testing (also referred to as an anal Pap smear); although the test's efficacy is still being reviewed. An HPV vaccine that protects against some strains of HPV – and possibly anal cancer – is becoming available, although it cannot treat existing infections. Depending on the severity of the individual case, those diagnosed with anal cancer will be treated with surgery, radiation, chemotherapy, or a combination.