Anal cancer is an uncommon type of cancer that occurs in the anal canal. The anal canal is a short tube at the end of your rectum through which stool leaves your body. Anal cancer is very different from colorectal cancer, which is much more common. Anal cancer, though rare, is a lump created by the abnormal and uncontrolled growth of cells in the anus. Most anal cancers (80%) are diagnosed in people who are over age 60. Prior to age 35, anal cancer is more common in men. However, after age 50, anal cancer is slightly more common in women.
The incidence rate of anal cancer is six times higher in single men as compared to married men. Receptive anal intercourse is strongly related to the development of anal cancer. Anal infection with human papillomavirus (HPV) resulting in genital warts is a major risk factor for the cancer.
Immunocompromised patients, such as those with HIV disease, are prone to get anal cancer. In this subgroup, the prognosis is worse, than for non-immunocompromised patients.
The most common symptom associated with anal cancer is bleeding. Itching at the anal opening may also be a symptom, although many people, initially, attribute such bleeding and itching to haemorrhoids. This can delay the diagnosis of anal cancer. Other signs and symptoms of anal cancer may include:
- Pressure in the anal area
- Unusual discharges from the anus
- Lump near the anus
- Change in bowel habits
Anal cancer occurs when a genetic mutation turns normal, healthy cells in the anal canal into abnormal cells. Healthy cells grow and multiply at a set rate, eventually dying at a set time. Abnormal cells continue to grow and multiply and do not die. The accumulating abnormal cells form a mass (tumour). Cancer cells invade nearby tissues and can separate from an initial tumour to spread elsewhere in the body (metastasize).
Anal cancer is closely related to a sexually transmitted infection called human papillomavirus (HPV). Evidence of HPV is detected in the majority of anal cancers. HPV is thought to be the most common cause of anal cancers.
Several factors have been found to increase the risk of anal cancer, including:
- Age: Most cases of anal cancer occur in people age 50 and older.
- Multiple sexual partners: People who have many sexual partners over their lifetimes have a greater risk of anal cancer.
- Anal Intercourse: People who engage in anal intercourse have an increased risk of anal cancer.
- Smoking: Smoking cigarettes may increase your risk of anal cancer.
- History of cancer: Those who have had cervical, vulvar or vaginal cancer have an increased risk of anal cancer.
- Human papillomavirus (HPV): HPV infection increases your risk of several cancers, including anal cancer and cervical cancer. HPV infection is a sexually transmitted infection that can also cause genital warts.
- Immunosuppressor Drugs or conditions that suppress immune system: People who take drugs to suppress their immune systems (immunosuppressive drugs), including people who have received organ transplants, may have an increased risk of anal cancer. HIV — the virus that causes AIDS — suppresses the immune system and increases the risk of anal cancer.
Tests and procedures used to diagnose anal cancer include:
- Anal canal and rectum examination for abnormalities: During a digital rectal exam, the doctor inserts a gloved, lubricated finger into your rectum. They feel for anything unusual, such as growths.
- Visual inspection of the anal canal and rectum: A short, lighted tube (anoscope) may be use to inspect your anal canal and rectum for anything unusual.
- Ultrasound of your anal canal: To create a picture of the anal canal, a probe, similar to a thick thermometer, may be inserted into your anal canal and rectum. The probe emits high-energy sound waves, called ultrasound waves, which bounce off tissues and organs in your body to create a picture. This picture helps evaluate anything abnormal.
- Biopsy: If any unusual areas are discovered, a small samples of affected tissue maybe taken and sent to a laboratory for analysis. By looking at the cells under a microscope, doctors can determine whether the cells are cancerous.
Once it’s confirmed that you have anal cancer, the doctor may recommend additional tests to determine whether your cancer has spread to your lymph nodes or to other areas of your body. This is called staging.
Tests may include:
The information from these procedures is used to assign the cancer a stage. The stages of anal cancer are indicated using Roman numerals ranging from 0 to IV, with the lowest stages indicating that the cancer is small and confined to the anus. By stage IV, the cancer has spread to distant areas of the body.
There are different ways to treat anal cancer, depending upon which stage it is in, if the patient has HIV or if the cancer is a recurrence. Doctors usually treat anal cancer with a combination of chemotherapy and radiation. Combined, these two treatments enhance each other and improve chances for a cure.
Radiation Therapy: It is a cancer treatment that uses high-energy X-rays or other types of radiation to kill cancer cells. There are two types of radiation therapy. External radiation therapy uses a machine outside the body to send radiation toward the cancer. Internal radiation therapy uses a radioactive substance sealed in needles, seeds, wires, or catheters that are led directly into or near the cancer. The way radiation therapy is given depends on the type and stage of cancer.
Chemotherapy: This is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing them or by stopping them from dividing. When chemotherapy is taken orally or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy). When chemotherapy is placed directly into the cerebrospinal fluid, an organ, or a body cavity such as the abdomen, the drugs mainly affect cancer cells in those areas (regional chemotherapy). The mode of administration of chemotherapy depends on the type and the stage of the cancer being treated.
Surgery: Doctors typically use different procedures to remove anal cancer based on the stage of the cancer:
- Surgery to remove early-stage anal cancers: Very small anal cancers may be removed through surgery. During this procedure, the surgeon removes the tumour and a small amount of healthy tissue that surrounds it. Since the tumours are small, early-stage cancers can sometimes be removed without damaging the anal sphincter muscles that surround the anal canal. Anal sphincter muscles control bowel movements, so doctors work to keep the muscles intact. Depending on the stage of the cancer, chemotherapy and radiation after surgery may be recommended
- Surgery for late-stage anal cancers or anal cancers that haven’t responded to other treatments: If the cancer hasn’t responded to chemotherapy and radiation, or if your cancer is advanced, your doctor may recommend a more extensive operation called abdominoperineal resection, which is sometimes referred to as an AP resection. During this procedure the surgeon removes the anal canal, rectum and a portion of the colon. The surgeon then attaches the remaining portion of your colon to an opening (stoma) in your abdomen through which waste will leave your body and collect in a colostomy bag.