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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\u2010based cohort study, the Norwegian Women and Cancer study (NOWAC). Exposure information was collected through postal questionnaires. Based on follow\u2010up 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 (<jats:italic>p<\/jats:italic> = 0.002) higher risk of breast cancer in former OC users, RR = 2.45 (95% CI 1.92\u20133.12), than among never users of OCs, RR = 1.67 (1.32\u20132.12). 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. \u00a9 2007 Wiley\u2010Liss, Inc.<\/jats:p>","DOI":"10.1002\/ijc.22699","type":"journal-article","created":{"date-parts":[[2007,3,19]],"date-time":"2007-03-19T20:37:52Z","timestamp":1174336672000},"page":"645-648","source":"Crossref","is-referenced-by-count":27,"title":["Hormone replacement therapy and breast cancer in former users of oral contraceptives\u2014The Norwegian Women and Cancer study"],"prefix":"10.1002","volume":"121","author":[{"given":"Eiliv","family":"Lund","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kjersti","family":"Bakken","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vanessa","family":"Dumeaux","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vegard","family":"Andersen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Merethe","family":"Kumle","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2007,5,25]]},"reference":[{"key":"e_1_2_5_2_2","doi-asserted-by":"publisher","DOI":"10.1016\/S1470-2045(05)70273-4"},{"key":"e_1_2_5_3_2","doi-asserted-by":"publisher","DOI":"10.1002\/ijc.20389"},{"key":"e_1_2_5_4_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0140-6736(03)14596-5"},{"key":"e_1_2_5_5_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0140-6736(96)90806-5"},{"key":"e_1_2_5_6_2","doi-asserted-by":"crossref","first-page":"1047","DOI":"10.1016\/S0140-6736(97)08233-0","article-title":"Breast cancer and hormone replacement therapy: collaborative reanalysis of data from 51 epidemiological studies of 52,705 women with breast cancer and 108,411 women without breast cancer. 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