Breast and colorectal cancer are two of the most common cancers affecting U.S. women. In 2007 in the United States, incidence rates of a new diagnosis of breast and colorectal cancer, respectively, were 1204 and 397 per 1,000,000 women (1). In addition, 228 and 141 per 1,000,000 U.S. women died of breast and colorectal cancers, respectively, in that same year (1). Although regular screening improves early detection and treatment and potentially reduces mortality (2-5), many U.S. women are not meeting recommendations for routine screening. The American Cancer Society (ACS) recommends that women receive a mammogram once a year beginning at age 40 years (6), and, until 2009, the U.S. Preventive Services Task Force also recommended that annual mammographic screening begin at age 40 (7). To detect colorectal polyps or cancer, ACS recommends that women and men receive either a virtual colonoscopy, double contrast barium enema, or flexible sigmoidoscopy every five years or a colonoscopy every 10 years beginning at age 50 years (6). Recent data from the National Health Interview Survey (NHIS), a representative sample of U.S. women, indicates only 53% of women 40 years and older received a mammogram in the past year (8) and 67% in the past two years (9), though among women ages 50-74 years, the percentage screened in the past two years reached 81% (10). The percentage of eligible women receiving regular sigmoidoscopies and/or colonoscopies is even smaller. NHIS data from 2008 show that among women ages 50 or older, 53% have ever received a sigmoidoscopy (9), and 50% have received either a sigmoidoscopy in the past five years or a colonoscopy in the past 10 years (8).

Underutilization of cancer screening has been found especially to affect socially marginalized and economically disadvantaged groups. Women with minority sexual orientation, such as lesbian and bisexual women, have been found in some studies to have lower screening rates than their heterosexual counterparts (11-13), though other studies have not found differences (14, 15). A recent review article found the literature to be mixed as to whether there are sexual orientation group disparities in mammographic screening (16). In a large sample of 93,311 women in the Women's Health Initiative (WHI), bisexual women aged 50 to 79 years were found to be slightly less likely to have received a mammogram in the past two years than same-age heterosexuals (82% vs. 84%) (11). Similarly, in a combined sample of 12,000 women from seven U.S. surveys of sexual minority women, 73% of women ages 40-49 years and 83% of women ages 50-75 years who described themselves as lesbian or bisexual reported ever receiving a mammogram, compared to an estimated 87-90% of women in U.S. general population surveys (13). One study examining colorectal screening rates by sexual orientation using data from the 2001-2008 Massachusetts Behavioral Risk Behavior Surveillance System (BRFSS) found no difference across sexual orientation groups in women ages 50 years and older having ever received colorectal screening (15).

Disparities in breast and colorectal screening rates also have been associated with household income, ethnicity, and state of residence. Women with lower household income have lower rates of breast and colorectal screening relative to higher household income (10, 17, 18). Lower rates of mammography have been found in Latina and American Indian/Alaskan Native women relative to white women (9, 10) and lower rates of colorectal screening have been found in Black and Asian women relative to white women (17, 19). Similarly, differences in health service use have been found to vary by geographic location within the United States due to the accessibility of care, state funding for health programs, and state policies on health insurance. The percentage of eligible women who received a mammogram in the past two years or ever received a colorectal screening varies by state. Among women ages 40 years and older, in general, those living in the Northeastern states, Florida, Minnesota, and Michigan have the highest rates of mammography in the past two years (range of 79%-85%) and women living in states in the South and West have the lowest rates (range 67%-73%) (18). Among women 50 years or older, lifetime colorectal screening rates are highest along the East Coast (62-74%), especially in the Northeast (68-74%), and lowest in the South and some Western states (53-58%) (17). Because household income, ethnicity, and state of residence are known to be important determinants of screening disparities, they must be accounted for in studies of sexual orientation patterns in screening adherence.

Institutionalized discrimination against sexual minority populations varies widely by state and includes state laws banning same-sex marriage and adoption of children by same-sex couples and the absence of laws protecting sexual minorities against hate crimes or employment discrimination (20, 21). These types of state-level institutionalized discrimination have been shown to negatively affect mental health of sexual minorities in nationally representative studies (22, 23), though it is not known if they also affect other health indicators, such as cancer screening.

Few studies have examined sexual orientation group differences in cancer screening, particularly colorectal screening, nor have they examined whether state of residence may modify any observed sexual orientation-related screening disparities. We undertook the present study to investigate sexual orientation group differences in breast and colorectal cancer screening in a large cohort of U.S. women and to assess whether screening adherence patterns are affected by state of residence.

From age 40 to 60 years, 85,756 women from the NHSII cohort (73% of original cohort) provided 360,264 observations included in our repeated measures analyses of mammographic screening (Table 1). From age 50 to 60 years, 32,831 women (87% of age-eligible women from the original cohort) contributed data to cross-sectional analyses of ever receipt of colonoscopy/sigmoidoscopy during this age period (Table 2). Approximately 1% of the cohort described themselves as lesbian or bisexual and 94% as white, and annual household income ranged from less than $50,000 (17%) to greater than $100,000 (35%). Sixty-two percent (n=31) of U.S. states had sexual-orientation-related protections in state law, and AHRQ overall health care quality rating scores in the states ranged from 26 to 69 with a mean of 48 (standard deviation=10), where lower score indicated worse overall health care quality in a state (not in table).

Overall, receipt of a mammogram in the past two years among women aged 40 and older was common though not universal and differed slightly by sexual orientation: heterosexual 84%; bisexual 79%; lesbian 82% (Table 1). Receipt of a mammogram in the past two years was similarly high across age, ethnicity, and income groups, though some disparities were observed. On the other hand, fewer than half of eligible women had ever received a colonoscopy or sigmoidoscopy during the age interval 50 to 60 years, and rates did not differ by sexual orientation: heterosexual 39%; bisexual 39%; lesbian 42% (Table 2). In addition, rates of colonoscopy and sigmoidoscopy were low across all age, ethnicity, and income groups and in only the older age group did more than half of women report this type of cancer screening (60% of women ages 55-60 years).

Results of a set of three multivariable models for mammography are shown in Table 3. Bisexual (prevalence ratio [PR] 0.94; 95% confidence interval [CI] 0.90, 0.98) and lesbian (PR 0.97; 95% CI 0.95, 1.00) women were slightly less likely to have had a mammogram in the past two years compared to heterosexual women, and these differences were essentially unchanged when the other individual-level and state-level covariates were added to models. Differences in mammographic screening by ethnicity and household income were similarly modest. Each 10-unit elevation of state-level AHRQ health care quality score was associated with a 2% higher likelihood of having had a mammogram in the past two years. Interaction terms between sexual orientation and state-level indicators were not statistically significant (P>0.05).

Table 4 shows results of a set of three multivariable models for colonoscopy/sigmoidoscopy. No significant differences in screening by sexual orientation or ethnicity were found with the exception of African American women, who were almost 30% more likely than white women to have ever received colorectal screening. Household income showed a strong positive association with likelihood of colorectal screening. Interestingly, living in a state with sexual orientation-related legal protections was associated with 8% higher likelihood of having received colorectal screening (age-adjusted model, Table 4), but this protective effect was completely attenuated in the fully adjusted model (Table 4). With each 10-unit elevation of state-level AHRQ health care quality score, likelihood of having had a colonoscopy/sigmoidoscopy increased by 9%. Interaction terms between sexual orientation and state-level indicators were not statistically significant (P>0.05).

Breast and colorectal cancer are among the most prevalent cancers in U.S. women, and screening technologies widely available in the United States offer effective methods for early detection. Adherence to regular screening guidelines, however, falls well short of recommendations, particularly for colorectal screening. Concerns have been raised that unequal health care access for sexual orientation minorities may affect screening, perhaps due to actual and anticipated discrimination in health care settings or to inequities in health insurance coverage due to discriminatory marriage laws at the state and federal level in the United States (29). In our large, national cohort of women, we found that mammographic screening was only slightly lower in sexual minority compared to heterosexual women. In addition, for colorectal screening, we did not find screening disparities by sexual orientation, though adherence to colorectal screening recommendations was low in women of all groups. Furthermore, we did not find evidence that the presence or absence of sexual orientation-related protections in state laws modified associations between sexual orientation and mammographic or colorectal screening adherence.

Findings from previous studies on disparities in mammographic screening have been mixed, with some reporting rates that were several percentage points lower in sexual minority women compared to heterosexuals (11-13) and some finding no group differences (14, 15). The only other study we are aware of that has examined colorectal screening in women by sexual orientation did not find differences, similar to our study (15). For the NHSII cohort overall, the percent receiving a mammogram in the past two years (approximately 84%) was only slightly higher than the percent (81%) among women ages 50-74 years in a nationally representative NHIS (10). In addition, for the NHSII cohort overall, the percent of women ages 50 to 60 years reporting having ever received a colonoscopy or sigmoidoscopy (approximately 40%) was somewhat lower than the percent of women in NHIS ages 50 and older having received sigmoidoscopy in the past five years or colonoscopy in the past 10 years (8, 9). In sum, though NHSII is made up of nursing professionals, we did not find evidence that mammographic or colorectal screening rates were notably higher in our cohort compared to nationally representative estimates.

We found lower rates of mammography in Latina and Asian women but not African-American women compared to white women, which is consistent with some previous research (9, 10). We found higher rates of colorectal screening in African American women compared to white women but no other ethnic differences. Our findings for colorectal screening are different from prior studies finding lower rates of colorectal screening in Black and Asian women relative to white women (19). Perhaps this difference in findings is due to the composition of NHSII, which is made up of women who are current or former nursing professionals. As expected based on previous studies (9, 17, 18), we found a positive gradient by household income for both screening types, where higher income was associated with higher likelihood of screening. We also found higher quality state health care rating, as per AHRQ, to be positively associated with likelihood of a woman receiving colorectal screening. This finding suggests that despite existence of colorectal screening technologies throughout the country, a woman's state of residence strongly predicts her likelihood of benefiting from this type of life-saving technology. Given that all participants in NHSII are or were professional nurses, and therefore might be relatively advantaged compared to the general population in terms of knowledge of and access to medical screening, these state-level differences are all the more disturbing.

The proportion of NHSII participants who described themselves as lesbian or bisexual make up roughly 1.2% of the cohort, which is similar to the proportion (1.4%) found in the WHI cohort, made up of women ages 50-79 years (11), though lower than the proportion (2.9%) found in the representative sample of women ages 18-64 years responding the Massachusetts BRFSS survey (15). As the Massachusetts BRFSS includes many women who are younger than those enrolled in NHSII or WHI, it is possible that these differences in proportion lesbian or bisexual represent historical cohort changes in the prevalence of sexual minority identity in U.S. women (30) or discomfort among the older cohorts of women with disclosing a minority sexual orientation identity on a survey.

Our study has several limitations. Our colorectal screening analyses included only colonoscopy and sigmoidoscopy, so colorectal screening rates in the cohort may have been higher if nonendoscopic screening were also included. Data were self-report. Because NHSII is composed predominantly of white women, and the socioeconomic range found in the cohort is narrower than in the country as a whole, generalizability may be reduced, though confounding by uncontrolled factors associated with ethnicity and socioeconomic status is also diminished. Women participating in NHSII were all registered nurses at enrollment and so may be expected to have higher rates of screening adherence than women not working in a health care profession. It is possible that the magnitude of sexual orientation disparities in screening could be different in a sample not made up of health professionals. Importantly, though, because all women in the cohort were registered nurses, comparisons across subgroups within the cohort are not biased by involvement in the nursing profession. In addition, sexual orientation was not a factor in recruitment into the cohort, therefore findings are not affected by this type of enrollment bias.

Concerns have been raised that unequal health care access for sexual orientation minorities may adversely affect cancer screening. These concerns are well-founded given the strong evidence of actual and anticipated discrimination in health care settings and inequities in health insurance coverage resulting from discriminatory marriage laws in U.S. states and in the federal government (29). Nevertheless, we found only slight disparities across sexual orientation groups in mammography and none in colorectal screening. It is important to note, however, that rates of colorectal screening were unacceptably low in women across all groups. The absence of sexual orientation disparities in a context of universally poor utilization of potentially life-saving colorectal screening technologies is not a reassuring finding. Rather, interventions are needed to increase screening in women of all social and income groups and across all states.