Anal cancer is a cancer of the anal canal that is pathologically a squamous cell carcinoma, usually originating from the human papilloma virus (HPV). It presents as a hard mass-like lesion near the anus and can grow into the rectovaginal septum or up into the rectum. It is diagnosed by biopsy and treated with radiation therapy and chemotherapy.
Anal cancer is fairly uncommon and accounts for about 1-2% of cancers affecting the intestinal tract. Approximately 1 in 600 men and women will get anal cancer in their lifetime (this can be compared to 1 in 20 men and women who will develop colon and rectal cancer in their lifetime). Unlike some cancers, the numbers of patients that develop anal cancer each year is slowly increasing, especially in some higher risk groups.
The anus, or anal canal, is the passage that connects the rectum, or last part of the large intestine, to the outside of the body. Anal cancer arises from the cells around the anal opening or in the anal canal just inside of the anal opening. Anal cancer originating in squamous cells unique to the anal canal is called squamous cell carcinoma. Other rare types of cancer may also occur in the anal canal, such as melanoma, and are treated differently than the typical squamous cell carcinoma.
Cells that are becoming malignant or premalignant but have not invaded deeper into the skin are referred to as high-grade anal intraepithelial neoplasia or HGAIN (previously referred to by a number of different terms, including "high-grade dysplasia," "carcinoma-in-situ,"anal intraepithelial neoplasia grade III, high-grade squamous intraepithelial lesion, or "Bowen's disease"). While this condition is likely a precursor to anal cancer, this is not anal cancer and is treated differently than anal cancer.
Anal cancer is commonly associated with infection with the human papilloma virus (HPV), but some anal cancers develop without this infection being present. HPV can also cause warts in and around the anus as well as genital warts (on the penis in men and the vagina or cervix in women), but warts do not have to be present for anal cancer to develop. HPV is also associated with an increased risk of cervical, vaginal or vulvar cancer in women, penile cancer in men, as well as with some head and neck cancers in men and women. Having some of these cancers, especially cervical or vulvar cancer (or even precancerous changes in the cervix or vulva), can put people at an increased risk for anal cancer, likely from the association with HPV infection.
Additional risk factors for anal cancer include:
Age - While most of the cases of anal cancer develop in people over age 55, one third of the cases occur in patients that are younger than that.
Anal sex - People participating in anal sex, both men and women, are at increased risk.
Sexually transmitted diseases - Patients with multiple sex partners are at a higher risk of getting sexually transmitted diseases like HPV and HIV and are therefore at an increased risk of developing anal cancer.
Smoking - Harmful chemicals from smoking increase the risk of most cancers, including anal cancer.
Immunosuppression - People with weakened immune systems, such as transplant patients who must take drugs to suppress their immune systems and patients with HIV infection are at a higher risk.
Chronic local inflammation - People with long-standing anal fistulas or open wounds in the anal area are at a slightly higher risk.
Pelvic radiation - People who have had pelvic radiation therapy for rectal, prostate, bladder, or cervical cancer are at an increased risk.
Although 20% of anal cancers may be asymptomatic, many cases of anal cancer can be found early by careful examination. It is important not to delay diagnosis if any anal symptoms persist beyond a few days. Anal cancers may cause symptoms such as:
Bleeding from the rectum or anus
Lump or mass at the anal opening
Persistent or recurring pain in the anal area
Persistent or recurrent itching
Change in bowel habits (having more or fewer bowel movements) or increased straining during a bowel movement
Narrowing of the stools
Discharge or drainage (mucus or pus) from the anus
Swollen lymph nodes (glands) in the anal or groin area
These symptoms can also be caused by less serious conditions such as hemorrhoids, but you should never assume this. If you have any of these symptoms, see your doctor or colon and rectal surgeon.
The diagnosis of anal canal cancer is largely based on clinical suspicion. Frequently, diagnosis is delayed simply because people think they have a bothersome hemorrhoid and begin hemorrhoid treatments. It is very important to have an accurate diagnosis and have a thorough examination if anal symptoms occur. Be sure to see a qualified medical professional and give a detailed history of your symptoms. Anal canal tumors can occur anywhere in the anal canal. Some low tumors can be visualized near the anal opening or anal verge, while many are higher and are not visible but are easily palpable on digital rectal examination. Some anal canal cancers grow into the rectovaginal septum, or the space between the vagina anteriorly and the rectum posteriorly. These tumors can be difficult to see, and usually require a digital examination that may include a careful palpation of this area to properly examine the length of the rectovaginal septum. Anal cancer is usually found on examination of the anal canal because of the presence of symptoms. A careful examination usually reveals an abnormality. The groin should be palpated for swollen lymph nodes. When an abnormal area is visualized or palpated, the area is then biopsied. This is usually done as an outpatient procedure, and can be done in conjunction with a colonoscopy if one has not been performed. The biopsy is then examined by a pathologist to determine the diagnosis of anal canal cancer. Once the diagnosis has been made, additional tests to determine the extent of the cancer may be recommended, which may include ultrasounds, X-rays, CT scan, and/or PET scan.
The staging of anal canal squamous cell carcinoma is based on the size of the tumor and lymph node metastasis. The American Joint Committee on Cancer has a well-developed TMN staging system where T stands for tumor, M stands for metastasis, and N stands for lymph nodes. The risk of nodal metastasis correlates with the size, depth of invasion and the histologic grade of the tumor. Nodal metastasis by T stage is estimated at 0% for T1, 8.5% for T2, 29% for T3, and 35% for T4 tumors. Tumors greater than 5 cm in size have lymph node metastasis 47% of the time. Lymphatic drainage of the upper anal canal is to superior rectal lymph nodes deep inside of the pelvis, while lymphatic drainage of the lower anal canal is to the inguinal and femoral nodes, often easily palpable in the groin creases. Distant metastasis to other organs can be found in the liver, lungs, bone, and subcutaneous tissues.
The treatment of squamous cell carcinoma of the anus rests on the location and extent of disease. If the cancer is small and does not involve the muscles of the anal canal, wide local excision may be an option. Tumors extending into the anal muscles without metastatic disease are treated with chemotherapy and radiation therapy without surgery to remove the tumor. Sometimes a diverting colostomy is needed if the rectal lumen is nearly obstructed, or the tumor has penetrated the rectovaginal septum. Advanced stage tumors are treated with chemotherapy and sometimes a diverting colostomy if there are obstructive symptoms. After the diagnosis and extent of disease is known, a treatment plan can be customized to fit your specific needs. If you decide to undergo the recommended chemotherapy, you will then have a port placed (which is a portal placed just under the skin in your upper chest) through which the chemotherapy medications are administered. This will need to be set up as an outpatient procedure. Chemotherapy is administered in an office setting or a specialized cancer center. Radiation therapy is administered at a radiation oncology center and is given during the same time period as the chemotherapy over the course of five to six weeks. Soon after diagnosis, patients can expect appointments with a radiation oncologist, medical oncologist and a surgeon for port placement. Fortunately, squamous cell carcinomas are very radiosensitive, meaning they generally melt away with radiation treatments. The addition of chemotherapy, which treats the entire body, has achieved cure rates of over 80%.