• Researchers used data from the Norwegian Women and Cancer Study to investigate an association between hormone replacement therapy (HRT) and oral contraceptive use with breast cancer risk. A total of 35,453 women were studied, all born between 1927 and 1957. More than one-third of the women had never used oral contraceptives or HRT and 36.6% were current users of HRT. The study found that without any adjustment for the effect of HRT use, current use of oral contraceptives was significantly associated to breast cancer risk. In the same way, current use of HRT, without any adjustment for oral contraceptive use, was significantly associated with an increase in breast cancer risk. Researchers divided current users in two groups of less than 5 years and 5 or more years of use, and found increasing risk with increasing duration of use. Postmenopausal women with current use of HRT had significantly higher risk of breast cancer if they were also former oral contraceptives users compared to women who had never used oral contraceptives.¹

¹Hormone Replacement Therapy and Breast Cancer in Former Users of Oral Contraceptives - The Norwegian Women and Cancer Study, International Journal of Cancer, 121, 645-648, 2007.