impossible for researchers to use this database to estimate the incidence and prevalence of cancer among sexual and gender minorities.

In 1999, when the Institute of Medicine report Lesbian Health was published, insufficient research had been conducted to determine whether lesbians were at greater risk for breast cancer than heterosexual women. Unfortunately, 12 years later the same is true. While the relative risk of breast cancer for lesbians and heterosexual women is the topic of much discussion, a definitive answer is still unavailable. It is believed that lesbians may be at higher risk for breast cancer because there is some evidence that they have a higher prevalence of certain risk factors, including nulliparity, alcohol consumption, smoking, and obesity. The evidence comes from a number of studies. Using cohort data from the Nurses’ Health Study II (NHSII), Case and colleagues (2004) compared women from the cohort who identified as lesbian (n = 694) or bisexual (n = 317) with the cohort’s heterosexual women (n = 89,812). They found that the lesbian and bisexual women were more likely to be nulliparous, were more likely to be overweight and obese (lesbians more so than bisexual women), had higher smoking rates, and were more likely to report having 60 or more alcohol-containing drinks a month. Diamant and colleagues (2000c) used data from the Los Angeles County Health Survey on 4,610 women who self-identified as heterosexual, 51 who self-identified as lesbian, and 36 who self-identified as bisexual. They found that the lesbians and bisexual women were significantly more likely to report tobacco use and were more likely to report drinking alcohol frequently and in greater quantities compared with the heterosexual women. Another study, using data from the California Health Interview Survey, a population-based telephone survey, found a significantly higher prevalence of cigarette smoking among self-identified lesbians (n = 343) and bisexual women (n = 511) than among heterosexual women (n = 24,830) (Tang et al., 2004). A more recent population-based study used aggregated data from the 2001–200 Massachusetts Behavioral Risk Factor Surveillance System surveys. The authors found that lesbians (n = 719) were more likely to be obese but not more likely to be overweight than heterosexual women (n = 39,701), while there were no significant weight differences between bisexual (n = 432) and heterosexual women (Conron et al., 2010). Although binge drinking was not defined in this study, it was found that lesbians and bisexual women were more likely to binge drink and be current smokers than their heterosexual peers. As some of these risk factors are associated with other cancers, most notably lung cancer (smoking), it is likely that women who have sex with women may be at greater risk for some cancers than heterosexual women.

It has long been established that men who have sex with men have a greater risk for anal cancer (Koblin et al., 1996). Anal cancer is associated

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