Anal cancer

Definition

Anal cancer is an uncommon form of cancer affecting the anus. The anus is the inch-and-a-halflong end portion of the large intestine, which opens to allow solid wastes to exit the body. Other parts of the large intestine include the colon and the rectum.

Demographics

Approximately 5,000 Americans were diagnosed with anal cancer in 2009, and an estimated 700 individuals died of the disease during this same interval, according to the American Cancer Society.


Anal cancers are fairly rare: they make up only 1% to 2% of cancers affecting the digestive system. This type of cancer is diagnosed much less frequently than cancers of the colon and rectum. The disease affects women somewhat more often than men. As the average age of the general population increases, the incidence of anal cancer is also increasing. The average age at diagnosis for most anal cancers is 60 years and older.



Description

Different cancers can develop in different parts of the anus, part of which is inside the body and part of which is outside. Sometimes abnormal changes of the anus are harmless in their early stages but may later develop into cancer. Some anal warts, for example, contain precancerous areas and can develop into cancer. Types of anal cancer include:

  • Squamous cell carcinomas-Most anal cancers diagnosed in the United States are squamous cell carcinomas, which arise from the cells lining the anal margin and the anal canal. The anal margin is the part of the anus that is half inside and half outside the body, and the anal canal is the part of the anus that is inside the body. The earliest form of squamous cell carcinoma is known as carcinoma in situ, or Bowen's disease.
  • Cloacogenic carcinomas-Often listed as a subclass of squamous cell cancer of the anus, these tumors develop in the transitional zone, or cloaca, which is a ring of tissue between the anal canal and the rectum. Other terms for this type of tumor are basaloid or transitional cell carcinoma of the anus.
  • Adenocarcinomas-A small percentage of anal cancers are classified as adenocarcinomas, which affect glands in the anal area.
  • Basal cell carcinoma or malignant melanoma-A very small percentage of anal cancers are either basal cell carcinomas, or malignant melanomas, two types of skin cancer. Malignant melanomas, which develop from skin cells that produce the brown pigment called melanin, are far more common on areas of the body exposed to the sun.

Two other very rare types of anal cancers are Paget's disease (not the same as Paget's disease of the bone) and gastrointestinal stromal tumors.

Risk factors

Most cases of squamous cell carcinoma of the anus appear to be linked to infection by the human papilloma virus (HPV). This same virus causes most cases of cervical cancer. Therefore, women who have been diagnosed with cervical cancer are considered to be at high risk for the development of anal cancer. HPV can be spread during vaginal, anal, and oral intercourse. The HPV subtype most likely to cause anal cancer is HPV-16. HPV subtypes HPV-6 and HPV-11 cause most cases of genital and anal warts.

Individuals infected with the human immunodeficiency virus (HIV) are also at increased risk for the development of anal cancer. A history of multiple sexual partners increases risk for HIV and HPV infection and also increases risk for anal cancer. Anal intercourse, especially in individuals younger than age 30, increases the risk for anal cancer in both men and women.
Smokers are at higher risk, as are individuals with weakened immune systems, such as transplant patients taking immunosuppressant drugs.

Causes and symptoms

The exact cause of most anal cancers is unknown. Symptoms of anal cancer resemble those found in other harmless conditions. They include pain, itching and bleeding, straining during a bowel movement, change in bowel habits, change in the diameter of the stool, discharge from the anus, and swollen lymph nodes in the anal or groin area.

Examination

Anal cancer is sometimes diagnosed during routine physicals, or during minor procedures such as hemorrhoid removal. It may also be diagnosed during a digital rectal examination (DRE), when a physician inserts a gloved, lubricated finger into the anus to feel for unusual growths. Digital rectal exams are typically done to check for prostate cancer and are sometimes part of routine pelvic exams in women.

Tests

Radiologic tests used to aid diagnosis include x ray, computed tomography (CT) scans, magnetic resonance imaging (MRI) and positron emission testing (PET) scans.

Procedures

Other diagnostic procedures for anal cancer include: anoscopy, which is a procedure that involves use of a special device to examine the anus; proctoscopy, a procedure that involves use of a lighted scope to see the anal canal; and transrectal ultrasound, which uses sound waves to create an image of the anus and nearby tissues.

A biopsy is performed on any suspicious growths; that is, a tiny specimen of the growth is removed and examined under a microscope for cancer cells. A procedure called a fine needle aspiration biopsy, in which a needle is used to withdraw fluid from lymph nodes located near the growth, may also be performed to make sure the cancer has not spread to these nodes.

Traditional

Anal cancer is treated using three methods, used either in concert or individually: surgery, radiation therapy, and chemotherapy. Two types of surgery may be performed. A local resection, performed if the cancer is small and has not spread, removes the tumor and an area of tissue around the tumor. A more extensive procedure, an abdominoperineal (AP) resection, is a more complex procedure in which the anus and the lower rectum are removed, and an opening called a colostomy is created for body wastes to exit. This procedure is fairly uncommon because radiation and chemotherapy are just as effective. AP resection may be used however, if radiation and chemotherapy are not effective or if the cancer recurs after treatment with radiation and chemotherapy.

Drugs

Chemotherapy fights cancer using drugs, which may be delivered via pill or needle. Some chemotherapy types kill cancer cells directly, while others act indirectly by making cancer cells more vulnerable to radiation. The main drugs used to treat anal cancer are 5-fluorouracil (5-FU) and mitomycin or 5-FU and cisplatin. Side effects of chemotherapy, which damages normal cells in addition to cancer cells, may include nausea and vomiting, hair loss, loss of appetite, diarrhea, mouth sores, fatigue, shortness of breath, and a weakened immune system.

Prognosis

Anal cancer is often curable. The chance of recovery depends on the stage of the cancer at the time of diagnosis and the patient's general health.

The overall five year survival rate for anal cancer is 60% in men and 78% in women. Five year relative survival rates for anal cancer diagnosed in localized stages is 89%, 61% for cancer diagnosed with regional spread, and 30% for individuals diagnosed with anal cancers that have already metastasized to distant sites in the body.

Prevention

Reducing the risks of the sexually transmitted diseases HPV and HIV also reduces the risk of anal cancer. Results of recent research indicate that as many as 80% of anal cancers could be prevented by vaccination against HPV subtypes 16 and 18. In addition, quitting smoking lowers the risk of anal cancer. In adults considered to be at low risk for anal cancer over the age of 50, screening as part of exams for colon cancer, prostate cancer, and during pelvic exams for women may lead to earlier detection if an anal tumor is present. Screening procedures specific to anal cancer may be recommended for members of high risk groups.