Anal cancer is relatively uncommon compared to other cancers. In the general population only 1.5 men per 100000 and 1.9 women per 100000 will develop anal cancer. In HIV positive people the estimated rates are between 46-131 men per 100000 people, and 30 women per 100000. HIV positive men who have sex with men have the highest rates, and African American men are much more likely than other men to develop it.
Almost all cases are in people over 35 years of age.
It is still unknown why HIV positive people undergoing retroviral therapy have increased rates of anal cancer. Compared to many other cancers anal cancer is usually slow to develop so it is possible that the increased life span provided by retrovirals allows more time for the cancer to develop.
Anal cancer is generally asymptomatic in the early stages, which is why screening is so important, especially for those at risk. Most people aren't aware they have anal cancer until later stages when they become symptomatic. When invasive cancer develops the primary reported symptoms are localized pain or tenderness, sometimes constant but sometimes only during bowel movements or receptive anal intercourse. Some patients experience bleeding with bowel movements or following sex that is different from their normal pattern. Some will feel a lump or hard area on the outside of the anal area that appears to be increasing in size. As tumors grow and begin to invade the sphincter muscle, pain is common and often patients experience a sense of fullness and a constant need to evacuate. If you are at risk of anal cancer and you begin to develop symptoms, then you should be examined promptly. Patients are urged to contact their doctor immediately if they begin to develop any symptoms.
When patients have symptoms related to anal cancer, something can almost always be felt by inserting a finger into the anus. Too often, the possibility of cancer is overlooked and symptomatic patients are told that it must be their hemorrhoids and not examined with a simple digital anal rectal examination (DARE). Sometimes patients are embarrassed and don't let their providers know they are having symptoms. Even in patients with no symptoms, something abnormal is usually felt with a DARE. Since many will have no symptoms, it is important for patients at risk to be examined regularly with DARE. If a mass, a thickening, an area of hardness, a lump, an area of localized tenderness or an ulcer is found, then the patient must be referred to clinicians experienced in managing anorectal problems who can evaluate and biopsy the suspicious areas.
Another way in which cancers are found is during routine HRA. The areas that appear the most worrisome or possibly suggestive of cancer are assessed and biopsied as patients are examined. We tend to biopsy ulcerated areas, thickened areas, and lesions containing abnormal vessels. Occasionally the biopsy will show superficially invasive or early cancer. It is unusual not to be able to feel something abnormal that correlates with the abnormality seen through the microscope, but the goal is to evaluate and to periodically biopsy the most abnormal appearing area seen during an exam. We do this because it is important to assess the severity of anal lesions and to rule out the possibility of invasion, which sometimes is not visually obvious even to an experienced clinician.
When caught in the early stages anal cancer responds well to treatment. Treatment usually entails chemotherapy and radiation, and sometimes surgery to remove cancerous tissue from the anus. Chemotherapy and radiation can be expected to cause tumors to completely regress in 80% to 90% of patients.