Abstract 794: Trends of ovarian cancer incidence by histotype and race/ethnicity in the U.S.: 1992-2017
Authors: Phung Minh Tung , Pearce Celeste Leigh , Meza Rafael , Jeon Jihyoun 
Published: July 2021

Abstract
Background: Ovarian cancer incidence rates in the U.S. decreased since the early 1970s, which was largely attributed to increasing parity among birth cohorts through 1935 and the introduction of combined oral contraceptives (COCs) in the 1960s. However, COC use prevalence has dramatically declined among 20-34 year-olds since the early 2000s as has parity. Ovarian cancer histotypes share many risk factors, including parity and COC use, but the magnitude of the effects differs by histotype. In addition, the prevalence of these risk factors differs by race/ethnicity. Understanding the trends in ovarian cancer incidence by histotype and race/ethnicity will allow us to consider the impact of changes in risk factor profiles.
Methods: Ovarian cancer incidence rates in 1992-2017 were obtained from the Surveillance, Epidemiology, and End Results (SEER) 13 registry. Age-standardized ovarian cancer incidence trends for the three most common histotypes (high-grade serous (HGS), endometrioid and clear cell) and four racial/ethnic groups (Hispanic, Asian/Pacific Islander (API), non-Hispanic Black (NHB), and non-Hispanic White (NHW)) were analyzed using joinpoint regression. Temporal trends of each histotype were analyzed using age-period-cohort models.
Results:
Joinpoint regression analysis: NHW had the highest incidence rates for HGS and endometrioid cancers, while API had the highest rate for clear cell cancer. HGS cancer incidence declined in all racial/ethnic groups during 1992-2017; NHW had the greatest reduction. Endometrioid cancer incidence decreased in NHW and NHB but increased in Hispanics in recent years. All racial/ethnic groups showed an increasing trend of clear cell cancer incidence.
Age-period-cohort analysis: HGS cancer incidence has been decreasing in NHW and API by birth cohort, but not in NHB or Hispanics. There is a decreasing trend in HGS cancer incidence by period in NHW, but no clear period-specific pattern was observed among other racial/ethnic groups. Endometrioid cancer incidence has been decreasing in NHW and API, but increasing in NHB and Hispanics in recent cohorts. Clear cell cancer incidence has been increasing by birth cohort in all racial/ethnic groups.
Conclusions: HGS and endometrioid cancer incidence has been decreasing overall, but clear cell cancer incidence has been increasing. This may be due to an improvement in diagnosis with a shift from classifying “carcinoma, not otherwise specified” to clear cell cancer. It is also possible that the impact of shifting patterns of lower COC use and parity are having a bigger impact on clear cell cancer given that these exposures are more protective for this histotype. Further, the introduction of opportunistic salpingectomy may balance any impact of COC use or parity changes for HGS cancer. There are differences in the ovarian cancer incidence trends by histotype and race/ethnicity, highlighting the impact of different preventive strategies.
Citation Format: Minh Tung Phung, Celeste Leigh Pearce, Rafael Meza, Jihyoun Jeon. Trends of ovarian cancer incidence by histotype and race/ethnicity in the U.S.: 1992-2017 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 794.