Anal Cancer: In Gay and Bisexual Men

Introduction
Anal cancer is a serious and pervasive health problem among and gay and bisexual men. Before the onset of the AIDS epidemic, the incidence of anal cancer among men with a history of receptive anal intercourse has been estimated at about 35 per 100,000. This is about the same incidence as that for cervical cancer prior to the implementation of broad screening programs promoting early detection and treatment among at-risk women.

As with many cancers, the exact causes of anal cancer are not clearly understood. However,there is general scientific consensus that human papillomavirus (HPV) is at least partly to blame.HPV is a sexually transmitted infection, found in many different types in different parts of the body.

Infection with HPV is common, with one large study at UCSF detecting HPV in 61% of HIV-negative and 93% of HIV-positive of gay and bisexual men. Typically, infection is with not one but several different types of HPV. In this same study, 23% of HIV-negative and 61% of HIV-positive men were infected with multiple HPV types. Several studies have suggested that having multiple types of HPV increases risk of progression to cancer.

The evidence for an association between HPV and anal cancer is strong. Similar to cervical cancer, the DNA for HPV is often detected in anal cancer tissues. The types of HPV detected are also those known to cause cancer. Conversely, anal cancer is rarely found without finding some type of HPV also present. Anal Squamous

Intraepithelial Lesions
Infection with HPV does not automatically result in the development of cancer; it may in fact result in no disease at all. Some people develop tissue abnormalities in the anus and not cancer. Several of these tissue abnormalities are not known to be harmful, but several are believed to be precursors to cancer.

Common Terms
These abnormalities are lesions or growths that occur in the surface layer of the skin (the epithelial layer) in the anus chamber (the squamous) and are described in two stages: low-grade squamous intraepithelial lesions (LSIL) and high-grade squamous intraepithelial lesions (HSIL). They are differentiated by size, shape, color, texture, and risk of further progression to cancer. Together they are referred to as anal squamous intraepithelial lesions (ASIL). Other terms sometimes used include “dysplasia” or “intraepithelial neoplasms”. (See Figure 1)