Oral contraceptive use and hormone replacement therapy together as a risk of breast cancer among postmenopausal women.

Objectives: The aim of this study was to determine the effects of oral contraceptive (OC) use and hormone replacement therapy (HRT) in postmenopausal women on the risk of breast cancer (BC). Methods: This is a case-control study among 552 postmenopausal women (median age 59 years, range 48-72) who underwent OC (N=121, 21.9%) and HRT (N=229, 41.5%) administration. Cases were 283 patients with confirmed pT1-2 pN0-1 BC, and controls were 269 age-matched women with no history of cancer or hormone-related diseases, followed prospectively for at least 2 years. The χ2 test and the Student’s t-test were used, and the relative odds ratios (OR) calculation at 95% confidence interval (CI) was also obtained. Results: A total of 73 (17.8%) cases and 48 (17.8%) controls (p=0.008) were former user of OC, while the HRT users were 138 (48.8%) and 91 (33.9%), respectively (p<0.001). The duration of therapy was (cases vs. controls) 22.5±20.5 vs. 35.1±40.2 months; p=0.08) for OC, and 43.7±30.2 vs. 30.6±23.5 months; p<0.001) for HRT. The relative OR was 1.72 (95% CI 1.12-2.22), and 1.91 (95% CI 1.34-2.62) for OC and HRT users, respectively, while the cumulative risk in patients who underwent both OC and HRT therapy was 4.39 (95% CI 2.35-4.56). Conclusions: Although our results must be cautiously interpreted, due to small number of patients, both duration of HRT and common exposure to OC and HRT could have potential impact in increasing risk of BC in postmenopausal women.