The relationship between hormone therapy use at the time of diagnosis of breast cancer and tumor characteristics.

Exposure to postmenopausal hormone therapy (HT) may affect the stage, histological type, and hormone receptor (HR) status of invasive breast cancer at the time of diagnosis. One thousand six hundred eighty-four women with newly diagnosed first invasive breast cancer were recruited to the "MBF Foundation Health and Wellbeing after Breast Cancer Study." Women using systemic HT estrogen (E) or E combined with progesterone (P) at the time of diagnosis of breast cancer were compared with those not using HT. Breast cancer tumor data were obtained from the Victorian Cancer Registry. Regression analysis was used to determine the associations between HT use or not at the time of diagnosis and tumor histology (ductal vs lobular), stage (I vs II, III, IV), HR status (ER+ or PR+ or both vs ER- or PR-). Of 1,377 women included in the analysis, 226 (16%) were using HT at the time of diagnosis. Of HT users, 20.4% had lobular breast cancer, 50% were stage I, and 85.8% had HR-positive tumors. Of non-users, 13.6% had lobular breast cancer, 48.2% were stage I, and 82.4% had HR-positive tumors. Use of systemic HT was associated with increased odds of having lobular compared with ductal breast cancer (OR = 1.75, 95% CI = 1.14-2.69, p = 0.01). There were no associations between HT use and either breast cancer stage or HR status. Women using systemic HT at the time of diagnosis were more likely to have lobular rather than ductal breast cancer compared with women not on HT.