Anal Cancer Causes and Risk Factors

Anal cancer is a tumor that develops in the tissues of the anal canal. The anus is at the end of the large intestine where food waste completes its journey through the digestive tract and exits the body in the form of stool.

Anal cancer is less common than other types of colorectal cancer, including colon cancer and rectal cancer. Even so, its incidence has been rising in recent years, which underscores the importance of awareness and early detection.

What causes anal cancer?

Scientists have confirmed that anal cancer forms when healthy cells in the anus undergo harmful cellular DNA changes that cause them to multiply uncontrollably or remain viable long after they should die. The excess cells then bind together and form masses, or tumors, which can potentially invade nearby lymph nodes and spread to distant organs. The underlying causes of the cellular mutations are unclear.

One theory suggests that anal cancer may be connected in some way to the human papillomavirus (HPV), a common sexually transmitted infection. This theory is based on the fact that HPV is found in nearly all patients who have anal cancer, especially the squamous cell type. HPV is the same virus that has been linked to cervical cancer, and studies show that women who have a history of cervical cancer have an increased risk of anal cancer. Nevertheless, the majority of patients with HPV do not develop anal cancer. Research is underway to clarify the role of HPV, if any, in the development of anal cancer.

Anal cancer risk factors

Scientists have identified several risk factors for anal cancer. A cancer risk factor is a characteristic, behavior or condition that, when present, increases the likelihood of developing a tumor.

Anal cancer risk factors that can be controlled

Some anal cancer risk factors are lifestyle-related behaviors that can be changed. For instance, having multiple sexual partners can significantly increase the risk of contracting HPV as well as human immunodeficiency virus (HIV), which has also been linked to anal cancer. Receptive anal intercourse also increases the risk of anal cancer in both men and women.

Smoking greatly increases the risk of anal cancer, and the higher the pack-year history, the higher the risk. The cancer-causing chemicals in tobacco smoke can travel from the lungs to other areas of the body, including the anus. Smoking can also impair the body’s immune system, making it less effective at fighting off HPV, HIV and other infections. Researchers have determined that quitting tobacco can reduce the risk.

Anal cancer risk factors that cannot be controlled

Other anal cancer risk factors are characteristics or conditions that cannot be changed. These include:

• Frequent anal fistulas – An abnormal opening may develop in the skin near the anus, leading to the inside of the anal canal in the colon.
• Recurrent anal irritation - Redness, swelling, soreness or itching may occur in and around the anus.
• Weakened immune system - Certain medications and conditions can interfere with the body’s ability to fight off infections.
• Other cancers - Cervical, vaginal or vulvar cancer in women and penile cancer in men can increase the risk of anal cancer.

Benefit from world-class care at Moffitt Cancer Center

The respected researchers and clinicians at Moffitt, a National Cancer Institute-designated Comprehensive Cancer Center, continue to learn more about the prevention, detection and treatment of anal cancer. As a result, we are continually improving outcomes and enhancing the lives of our patients.

If you would like to learn more about anal cancer causes and risk factors, you can request an appointment with a specialist in the Gastrointestinal Program at Moffitt by calling 1-888-663-3488 or submitting a new patient registration form online. We do not require referrals.