Abstract
Estrogen receptor (ER)-positive breast cancer patients treated with tamoxifen are known to have an elevated risk of subsequent endometrial cancer. However, it is unclear if ER-negative patients also have a higher risk of endometrial cancer. This population-based study aims to evaluate whether breast cancer patients with distinctive ER and PR status possess differential risks in developing delayed endometrial malignancy. Data were obtained from the Surveillance, Epidemiology, and End Results program (1992-2009). Standardized incidence ratio (SIR) was calculated as the observed cases of endometrial cancers among breast cancer survivors compared with the expected cases in the general population. Data were stratified by latency periods, race, age, and calendar year of breast cancer diagnosis. We identified 2044 patients who developed a second primary endometrial cancer among 289,933 breast cancer survivors. The overall SIRs for subsequent endometrial cancers were increased in all of the four subtypes (ER+PR+, ER+PR-, ER-PR+, and ER-PR-) of breast cancer. SIR was increased for all latency periods except for the initial 6-11 months after breast cancer diagnosis. Stratifying by age of diagnosis, elevated SIRs in all ER/PR groups were statistically significant among patients diagnosed with breast cancer after the age of 40. Demographically, non-Hispanic whites had increased SIRs in all subtypes of breast cancer, while Hispanic whites had no statistically elevated SIRs. Here we showed that patients with invasive breast cancer have a higher risk of developing subsequent endometrial cancer regardless of ER or PR status. The increased risk among hormone receptor-negative breast cancer survivors raises concerns whether common etiological factors among these breast cancer subtypes increase the susceptibility to develop endometrial cancer. Lower threshold for routine endometrial cancer surveillance may be warranted.
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