Combined estrogen-progestin menopausal therapy (HRT) and combined estrogen-progestin contraceptives (OC) both increase breast cancer risk during current use and a few years after. We investigated risk of breast cancer in women who were users of HRT dependant on former history of OC use in a large, national population-based cohort study, the Norwegian Women and Cancer study (NOWAC). Exposure information was collected through postal questionnaires. Based on follow-up of 30,118 postmenopausal women by linkage to national registers of cancer, deaths, and emigration we revealed 540 incident breast cancer cases between 1996 and 2004. Compared to never users of either drugs current use of HRT gave a significant (p = 0.002) higher risk of breast cancer in former OC users, RR = 2.45 (95% CI 1.92-3.12), than among never users of OCs, RR = 1.67 (1.32-2.12). Relative risk of current use of HRT was similar for estrogen only and combinations with progestin added in ever users of OCs. The increased risk of breast cancer in current HRT users with a history of former OC use could have potential great impact on postmenopausal breast cancer risk as the proportion of postmenopausal women with former OC use will continue to increase.
hormone replacement therapy breast cancer former oral contraceptive users, combined estrogen progestin HRT OC breast cancer risk cumulative, Norwegian Women Cancer Study NOWAC breast cancer hormonal exposure, sequential hormonal exposure oral contraceptives HRT breast cancer, Lund Bakken postmenopausal breast cancer former OC use, population-based cohort study HRT breast cancer Norway, estrogen progestin combined therapy breast cancer incidence, cumulative hormonal exposure contraceptives menopause breast cancer risk, lifetime hormone use oral contraceptive HRT cancer interaction, current HRT use breast cancer relative risk former OC users
PMID 17372914 17372914 DOI 10.1002/ijc.22699 10.1002/ijc.22699
Cite this article
Lund, E., Sletten Bakken, K., Dumeaux, V., Andersen, V., & Kumle, M. (2007). Hormone replacement therapy and breast cancer in former users of oral contraceptives--The Norwegian Women and Cancer study. International journal of cancer, 121(3), 645-648. https://doi.org/10.1002/ijc.22699
Lund E, Sletten Bakken K, Dumeaux V, Andersen V, Kumle M. Hormone replacement therapy and breast cancer in former users of oral contraceptives--The Norwegian Women and Cancer study. Int J Cancer. 2007;121(3):645-648. doi:10.1002/ijc.22699
Lund, Eiliv, et al. "Hormone replacement therapy and breast cancer in former users of oral contraceptives--The Norwegian Women and Cancer study." International journal of cancer, vol. 121, no. 3, 2007, pp. 645-648.
Keywords
Contraceptives, Oral
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