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Aromatase inhibitors, tamoxifen, and endometrial cancer in breast cancer survivors
Author(s) -
Chlebowski Rowan T.,
Schottinger Joanne E.,
Shi Jiaxiao,
Chung Joanie,
Haque Reina
Publication year - 2015
Publication title -
cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.052
H-Index - 304
eISSN - 1097-0142
pISSN - 0008-543X
DOI - 10.1002/cncr.29332
Subject(s) - medicine , endometrial cancer , tamoxifen , hazard ratio , breast cancer , aromatase inhibitor , oncology , aromatase , gynecology , cancer , incidence (geometry) , confidence interval , obstetrics , physics , optics
BACKGROUND The risks of both endometrial cancer and postmenopausal breast cancer are increased by obesity and higher endogenous estrogen levels. Although aromatase inhibitors reduce breast cancer incidence, their influence on endometrial cancer is uncertain. METHODS The authors investigated this issue in a cohort of 17,064 women who were diagnosed with hormone receptor‐positive breast cancer in an integrated group practice health plan. Information on demographics, comorbidities, and the receipt of adjuvant endocrine therapy was available from electronic medical records and pharmacy records, respectively. Endometrial cancer information was obtained from the health plan's Surveillance, Epidemiology, and End Results‐affiliated tumor registry, and rates were compared across endocrine therapy groups (aromatase inhibitor, n = 5303; tamoxifen, n = 5155; switchers: both [n = 3787] or none [n = 2819]) using multivariable adjusted Cox proportional‐hazards models. RESULTS Endometrial cancer incidence was a statistically significant 48% lower in the aromatase inhibitor group versus the tamoxifen group (hazard ratio, 0.52; 95% confidence interval, 0.31‐0.87; P = .01). Endometrial cancer incidence was 29% lower in the aromatase inhibitor group versus the no endocrine therapy group (hazard ratio, 0.71; 95% confidence interval, 0.37‐1.35; P = .30) and 33% lower in the aromatase inhibitor group versus the tamoxifen group (hazard ratio, 0.67; 95% confidence interval, 0.42‐1.06; P = .08), but neither difference was statistically significant. Associations were stronger among those with good drug adherence. CONCLUSIONS In a community‐based, integrated health plan setting, endometrial cancer incidence was lower in women who were receiving an aromatase inhibitor compared with those who were receiving tamoxifen. In addition, aromatase inhibitors may mitigate the incidence of tamoxifen‐associated endometrial cancer. Although there were somewhat fewer endometrial cancers in the aromatase inhibitor group versus the no endocrine therapy group, further studies are needed for the definitive assessment of this potential association. Cancer 2015;121:2147–2155. © 2015 American Cancer Society .