with infection by the human papillomavirus (HPV), which is often sexually transmitted (Ryan et al., 2000), and individuals practicing receptive anal intercourse are at a higher risk for this infection (Daling et al., 2004). People with AIDS are at an increased risk for HPV-associated cancers, including anal cancer (Chaturvedi et al., 2009), although it is not known whether this greater risk is associated with AIDS-related immunosuppression or other cofactors for such cancers. In a study involving four cities, 1,218 HIV-negative men who have sex with men were tested for anal HPV, which was detected in 57 percent of the sample (Chin-Hong et al., 2004). In this study, a history of receptive anal intercourse and five or more male sex partners in the preceding 6 months appeared to be predictive of HPV infection. Other studies have shown prevalence rates of HPV infection in HIV-negative gay and bisexual men ranging from 61 to 78 percent (Friedman et al., 1998; Palefsky et al., 1998). Among HIV-positive homosexual and bisexual men, the prevalence of anal HPV infection may be as high as 93 percent (Palefsky et al., 1998). Unlike the prevalence of cervical HPV infection, which peaks during the third decade of life in women, the prevalence of anal HPV infection is steady throughout the life course of men who have sex with men, well into the sixth decade of life (Chin-Hong et al., 2004).

Similar to screening for cervical cancer, screening for anal cancer may be performed with cytology to detect HPV-associated disease (Palefsky, 2009). Currently, there exist no guidelines recommending routine anal cancer screening and no consensus on the optimal method or frequency of such screening (Palefsky, 2009). Some studies have recommended screening HIV-negative homosexual and bisexual men every 2 or 3 years (Goldie et al., 2000) and screening HIV-positive homosexual and bisexual men annually (Goldie et al., 1999). To date, however, there have been no randomized clinical trials evaluating many aspects of anal cancer screening, and the natural history of progression from precursor lesion to cancer is unknown (Wong et al., 2010).

Research on cancer among the transgender population has been extremely limited. For example, there have been no long-term prospective studies of breast cancer among transgender women. However, case reports have been published of breast cancer among transgender women who have taken feminizing hormones (Ganly and Taylory, 1995; Pritchard et al., 1988; Symmers, 1968) and transgender men who have taken masculinizing hormones and undergone chest surgery, as some breast tissue remains after such surgery (Burcombe et al., 2003; Eyler and Whittle, 2001). Transgender men on testosterone therapy may be at increased risk for ovarian cancer (Hage et al., 2000; Pache et al., 1991), and cases of prostate cancer have been reported among transgender women taking feminizing hormones (Markland, 1975; van Haarst et al., 1998).

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