Anal cancer occurs in the anus, the end of the gastrointestinal tract. Anal cancer is very different from colorectal cancer, which is much more common. Anal cancer's causes, risk factors, clinical progression, staging and treatment are all very different from colorectal cancer. Anal cancer is a lump which is created by the abnormal and uncontrolled growth of cells in the anus.
Anal cancer is very rare. According to the American Cancer Society, there were an estimated 7,270 new cases of anal cancer in the USA in 2014 (a rise from 5,070 in 2008). Of these, 4,630 were women and 2,640 were men. Approximately 1,010 people died from anal cancer in the USA in 2014.1
Reports suggest that the incidence of this type of cancer is rising. The number of anal cancer cases is increasing in both sexes, particularly among American men, and changing trends in sexual behavior - combined with current tobacco use and infection by a specific strain of the human papillomavirus - may help explain the increase, as this article explains.
Most anal cancer patients are diagnosed in their early 60s. Anal cancer is more common among women, men who receive anal intercourse, and people with weakened immune systems. Experts say that anal cancer is closely associated with some HPV (human papilloma virus) strains.
The anus, the anal canal and squamous cell carcinomas
The anus is right at the end of the gastrointestinal tract - the area right at the end. While the anal canal is the tube that connects the rectum to the outside of the body. The anal canal is surrounded by the sphincter - a muscle. The sphincter controls bowel movements by contracting and relaxing. In short, the anus is the outside area while the anal canal is the tube.
The anal canal is lined with squamous cells - flat cells that look like fish scales under the microscope. The majority of anal cancers develop from these squamous cells. Such cancers are known as squamous cell carcinomas.
The point at which the anal canal meets the rectum is called the transitional zone. The transitional zone has squamous cells and glandular cells - these produce mucus which helps the stool (feces) pass through the anus smoothly. Adenocarcinoma (type of cancer) of the anus can develop from these glandular cells. However, squamous cell carcinomas make up the vast majority of anal cancers.
Symptoms of anal cancer
Common symptoms of anal cancer may include:
- Rectal bleeding - the patient may notice blood on feces or toilet paper.
- Pain in the anal area.
- Lumps around the anus. These are frequently mistaken for piles (hemorrhoids).
- Mucus discharge from the anus.
- Jelly-like discharge from the anus.
- Anal itching.
- Change in bowel movements. This may include diarrhea, constipation, or thinning of stools.
- Fecal incontinence (problems controlling bowel movements).
- Women may experience lower back pain as the tumor exerts pressure on the vagina.
- Women may experience vaginal dryness.
Causes of anal cancer
Experts cannot comprehensively say what causes anal cancer. However, the following are considered as possible risk factors:
- HPV (human papilloma virus) - some types of HPV are closely linked to anal cancer. Approximately 80% of patients with anal cancer are infected in the anal area with a HPV.
- Sexual partner numbers - this is also linked to HPV. The more sexual partners somebody has (or has had) the higher are the chances of being infected with HPV, which is closely linked to anal cancer risk.
- Receptive anal intercourse - both men and women who receive anal intercourse have a higher risk of developing anal cancer. HIV-positive men who have sex with men are up to 90 times more likely than the general population to develop anal cancer, this study revealed.
- Other cancers - women who have had vaginal or cervical cancer, and men who have had penile cancer are at higher risk of developing anal cancer. This is also linked to HPV infection.
- Age - the older somebody is the higher is his/her risk of developing anal cancer. In fact, this is the case with most cancers.
- A weak immune system - people with a weakened immune system have a higher risk of developing anal cancer. This may include people with HIV/AIDS, patients who have had transplants and are taking immunosuppressant medications.
- Smoking - smokers are significantly more likely to develop anal cancer compared to non-smokers. In fact, smoking raises the risk of developing several cancers.
- Benign anal lesions - IBD (irritable bowel disease), hemorrhoids, fistulae or cicatrices. Inflammation resulting from benign anal lesions may increase a person's risk of developing anal cancer.
On the next page we look at how anal cancer is identified and the treatments available to those people who are diagnosed with anal cancer.