Anal Cancer Facts

Anal cancer facts*

High-risk HPV infection of the anal lining tissues is the most common cause of anal cancer.
High-risk HPV infection of the anal lining tissues is the most common cause of anal cancer.

*Anal cancer facts medical author: Charles P. Davis, MD, PhD

  • The anus is the end portion of the gastrointestinal tract. It includes the anal canal containing the muscular valve, or sphincter, which controls the emptying of the rectum to the outside. It also includes the perianal skin just outside of the anus.
  • Anal cancer is a disease in which human papillomavirus develops in the cells of the anus at the lower and external end of the digestive tract. Anal cancer can arise in either the anal canal or on the perianal skin.
  • Colorectal cancer is cancer that occurs in the part of the digestive tract in the colon or rectum. It is a much more common and completely different cancer type and is thus distinct from anal cancer.
  • Risk factors for anal cancer include age over 50, human papillomavirus (HPV) infection, many sexual partners, receptive anal sex, chronic immune suppression, and cigarette smoking.
  • The causes for anal cancer are HPV infection with certain types of HPV viruses, a weakened immune system, a history of certain prior pelvic cancers, and cigarette smoking.
  • Symptoms and signs of anal cancer include anal bleeding, pain or pressure in the anal area, lump or mass near the anus, anal discharge, and change in bowel habits.
  • Diagnostic tests include health history and rectal exam, anoscopy, and likely also deeper endoscopic examinations. Ultimately, a surgical biopsy may be performed to diagnose anal cancer.
  • The prognosis of anal cancer is affected by the stage, or extent, of the cancer when it was discovered. Stage is assessed by the results of the diagnostic tests, as well further testing involving CT scan and sometimes PET scan, and other health studies.
  • There are five stages of anal cancer ranging from 0 through IV. The higher the number, the more extensive the disease at presentation.
  • Treatment for anal cancer is usually curative when the disease is found at an early (lower numbered) stage. Today the best medical approach for the majority of patients is a combination of radiation and chemotherapy.
  • Surgery for very early disease also can be curative. Radical surgery requiring a colostomy is no longer a necessary initial or primary treatment. It may be required if there is residual or recurrent disease after nonsurgical treatment.
  • Stage IV or metastatic anal cancer is generally not curable, but treatment can both prolong survival with and reduce symptoms from the disease.
  • HPV vaccination may prevent this disease.

Anal anatomy

The anus is the lowest end of the gastrointestinal (GI) tract. It is the opening through which stool, or fecal matter, normally passes. The anal canal extends from the lower end of the rectum to the skin; this is where anal cancer occurs while colorectal cancer occurs in the rectum and colon. This canal is surrounded by muscles forming the internal and external anal sphincters that allow us to control when we defecate, or have a bowel movement. The perianal skin surrounds the anus in the perineal region behind either the vaginal orifice or the scrotum.

What is anal cancer?

The cancer cells arise in areas of the body when some of the cells of a tissue become abnormal in both their gross and microscopic appearance and in their behavior. These malignant cells can damage adjacent healthy tissue cells by directly invading them. Cancer cells also have the ability to invade blood vessels and lymphatic channels and spread, or metastasize, to other parts of the body.

While anal cancer begins in the anus, people sometime confuse it with colorectal cancer, which occurs in the colon and/or rectum.

What are the different types of anal cancer?

The majority of primary cancer of the anus are squamous cell carcinomas. Other types of anal cancers include

  • cloacogenic (also called basaloid or transitional anal cancer),
  • adenocarcinoma of the anal glands, and
  • melanoma (rare).

What are other types of anal masses or growths?

Not all growths in the anal region are cancers. A benign growth of tissue on a short stalk is called a pedunculated polyp. A flat-bottomed growth is called a sessile polyp. The sessile polyps are more likely to show precancerous or cancerous change microscopically.

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Medically Reviewed on 2/6/2020
References
"Anal Cancer." American Cancer Society.

Edge, S.B., et al. "Anal Cancer." AJCC Cancer Staging Manual, 7th Ed. New York, NY: Springer, 2010.

"NCCN Clinical Practice Guidelines in Oncology: Anal Carcinoma." Version 1.2017.

"PDQ National Cancer Institute Summaries: Anal Cancer." 2017.

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