br In agreement with existing literature
In agreement with existing literature, we found that Chinese, Filipino, and Japanese women indeed had higher incidence of clear cell ovarian cancer. Endometriosis could partly explain this given that it is a strong risk factor for the clear cell histotype . Miyazawa reported the highest hospital admission rates for endometriosis among Japanese women in comparison to non-Japanese Asian ethnicities and non-Asian races . Similarly, a retrospective cohort study based on electronic medical records of infertility clinic patients observed women of Filipino and Japanese origin to be more likely to have endometriosis than NHW women . Given that endometriosis is also a risk factor for en-dometrioid ovarian cancer, we would expect to see a higher incidence of the endometrioid histotype among these Asian American ethnic
groups in our results. However, this was not observed, which may be due to other ovarian cancer etiologic factors with histotype-specific effects.
The ASIRs for all Asian American ethnic groups were statistically significantly lower than those of NHWs after age 50, which has been observed in previous work . Again, the age-specific incidence pat-tern for Asian Indians/Pakistanis appeared to diverge from the other Asian subgroups since their ASIRs continued to increase after age 50 mimicking that of NHWs (Fig. 3). Given the timing of these observa-tions, the racial/ethnic differences in these patterns may be related to menopause given that menopausal symptoms, lifestyles, and behaviors during and after the menopause transition have been shown to differ by race/ethnicity [27,28], and such factors could differentially impact disease incidence. For example, differences in the prevalence of post-menopausal hormone therapy use by race has been noted, with White women being more commonly prescribed hormone therapy than other races . Also, the specific effect of hormone therapy and other fac-tors on ovarian cancer risk could vary by race; Peres et al. found sig-nificant heterogeneity in the association between reproductive, hor-monal, and lifestyle factors and ovarian cancer by race, such as parity being more protective for Asian women . Such variation across the Asian ethnic groups is likely, but there is limited reporting on this, highlighting the need for greater AEB071 in clinical and epidemiologic studies.
It has been noted that incidence rates of ovarian cancer has either remained unchanged or only slightly decreased among the aggregated Asian American women, contrary to the significantly greater decline that has been observed among NHW women [31–34]. However, when
Age-specific incidence rates of ovarian cancer by race/ethnicity, 1990–2014.
Abbreviation: ASIR = age-specific incidence rate; IRR = incidence rate ratio, CI = confidence interval.
we disaggregate the Asian American population, we observed incidence to be significantly decreasing for Chinese and Japanese women as well. Interestingly, increases in ovarian cancer incidence have been reported in both China [35,36] and Japan [37–39]. However, those living in the U.S. are likely to be different from those living in their native countries with respect to socioeconomic and lifestyle factors , as the ovarian cancer incidence differential between Japanese American and Chinese American women is much less than the reported two-fold between Japan and China [1,4,5]. Redaniel et al. also found significant ovarian cancer survival differences between Philippine residents and Filipino-Americans , underlying possible environmental mediations.
The lack of readily available cancer data, as well as population data, by detailed Asian ethnicity coupled with the rareness of ovarian cancer are often why most ovarian cancer research evaluates Asians in the aggregate. By leveraging the population-based SEER registry database, we are able to provide valuable insights into ovarian cancer incidence patterns and trends among the heterogeneous Asian American popu-lation with disaggregated ethnic groups. A limitation of such popula-tion-based studies is possible misclassification of race/ethnicity given that this information is primarily based on medical records . However, studies comparing administrative databases to self-report have shown low misclassification even when specific Asian ethnicities were considered [42,43]. The agreement between our findings and supporting literature adds to our confidence in the quality of data used in the analysis. In addition, we did not correct for salpingo-oophor-ectomy in our rate calculations, which underestimates the true in-cidence of ovarian cancer. However, prior incidence correction by Merrill that took into account the impact of this surgical procedure on ovarian cancer rates showed the biggest impact on NHWs and the smallest impact on Asians, suggesting an even greater disparity between the two . Ethnic-specific salpingo-oophorectomy rates would be useful given that they may differ by Asian American subgroup, which could explain some of our findings despite salpingo-oophorectomy’s small impact on Asians as a whole. However, current data on this is sparse, hence future work in this area could refine our understanding of ovarian cancer incidence rates among the Asian American ethnic po-pulations.