Anal Cancer

Anal cancer is a rare disease comprising only 1 to 5 percent of all carcinomas of the colon, rectum and anus. The American Cancer Society estimates that 5,260 anal cancer cases were diagnosed and approximately 720 attributable deaths occurred in 2010.  The incidence of anal cancer in the United States has increased significantly over the past 2 to 3 decades.

What causes anal cancer?
Epidemiological and molecular-biology studies have now shown that sexually transmitted infection with human papillomavirus (HPV) is the most important cause of anal cancer.

What are the risk factors for anal cancer?

  • human papillomavirus (HPV) infection
  • anoreceptive intercourse
  • cigarette smoking
  • immunosuppression following solid organ transplant
  • HIV infection

The annual incidence of anal cancer is approximately 6 per 100,000 in the heterosexual population; however, this incidence is much higher (up to 70 per 100,000) in HIV positive gay men.

Patients receiving chronic immunosuppressive therapy after solid organ transplant are at a higher risk for squamous cell carcinomas of many sites, including the anal canal.  This is likely the result of persistent HPV infection.  The risk is not insignificant, with at least one study demonstrating a 100-fold higher risk for anal cancer following renal transplantation.  (Clark et al Lancet 2004).

What are the symptoms of anal cancer?
Signs of anal cancer include pain, bleeding from the anus or rectum, an anal mass, and/or new onset of fecal incontinence. Most patients with anal cancer have rectal bleeding.  Diagnosis is often delayed because this type of bleeding can be ascribed to hemorrhoids.  Prompt evaluation by a colon and rectal surgeon is advised.

How is anal cancer diagnosed?
Once an anal mass is detected on examination in the office, it is important to proceed to the operating room for full evaluation.  It is important to determine the size of the tumor, biopsy the tumor and determine if there is sphincter involvement.  Anal cancer can also spread to the lymph nodes in the groin; therefore, this should be included in the full examination.

Once the diagnosis is confirmed, further staging of the tumor is done with a CAT scan of the abdomen and pelvis as well as a PET scan.  Other tests may include anal ultrasound and Magnetic Resonance Imaging, or MRI.

How is anal cancer treated?
Primary treatment of cancer of the anus is combined radiation and chemotherapy.  Once the treatment has been completed, it is critical that patients follow up routinely with their colorectal surgeon for anorectal examination in the office.  Surgical resection would be warranted in the event of residual or recurrent cancer.