1. Compared to Asian immigrants, American-born Asian women are more likely to develop Type I (estrogen-dependent) endometrial adenocarcinoma.
2. Among Asian women, being born in America is an independent risk factor for development of Type I endometrial cancer.
Evidence Rating Level: 2 (Good)
Study Rundown: Endometrial cancer is the most common gynecologic malignancy, with an incidence of nearly 50,000 new cases diagnosed each year. Endometrial cancer comes in two types. Type I is driven by excess estrogen production, usually endogenous (obesity-driven peripheral conversion of estrogen) such that rates are highest in industrialized countries. Type II is estrogen-independent, more aggressive and likely driven by genetics. In determining the extent to which nature vs. nurture determines cancer susceptibility, previous investigations have examined rates of various cancers among immigrants compared to American-born members of the same ethnicity. Prior research demonstrates an increased incidence of breast and gynecologic malignancies among American-born compared to immigrant Asian women. Yet, little is known about differences in risk of Type I and Type II endometrial cancers in these groups. In this study, researchers compared the proportion of Type I to Type II endometrial cancers among American-born Asian women and immigrant women. Findings demonstrate that Type I endometrial cancer was more common among American-born Asian women and also that the incidence of Type I disease increased over time, suggesting that the cancer-promoting risk factors related to being American-born are becoming more impactful over time.
Limitations include retrospective design, which creates opportunity for bias. Additionally, this study did not examine other common risk factors for endometrial cancer (nulliparity, anovulation, hypertension) and notably did not evaluate BMI. However, the relationships identified herein have strong foundation of biologic plausibility. Strengths include large sample size and nationally representative sample, increasing applicability of results. Future investigations might employ a prospective design and collect data on risk factors (BMI, ovulatory dysfunction, family cancer history) to better address this research question.
In-Depth [cross-sectional study]: Used data from the Surveillance, Epidemiology and End Results (SEER) database to examine information of 4,834 women from Utah, Hawaii, Iowa, New Mexico, Connecticut, Alaska, and the cities Detroit, San Francisco/Oakland, Seattle, Atlanta, San Jose/Monterey and Los Angeles. Asian women included those who self-identify as Chinese, Filipino, Japanese, Korean, South-East Asian and Indian descent. Type I cancers were defined as grade 1 or 2 endometrioid carcinomas. Type II cancers were defined as grade 3 endometrioid, clear cell or serous.
Among Asian women, being born in America is an independent risk factor for development of Type I endometrial cancer (HR: 1.95, CI:1.73-2.20; p<0.01). Over the study period (2001-2009), the incidence of Type I endometrial adenocarcinoma in American-born Asian women increased from 61% to 68% (p<0.01). The 5-year disease specific survival rates of Type I endometrioid carcinoma were the same for both groups (92%).
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