A new study has reported that tamoxifen significantly reduces the risk of a second cancer developing in the unaffected breast for women who carry either the BRCA1 or BRCA2 mutation. The findings were published online on August 5 in the Journal of Clinical Oncology by researchers at the Peter MacCallum Cancer Centre in Victoria, Australia
Women with the BRCA1 or BRCA2 mutation are much more likely to develop breast and ovarian cancer than other women. Some, like Angelina Jolie, will opt to have their breasts removed before a cancer develops, which reduces breast cancer risk by more than 95%. The new study evaluated women with these mutations conducted a study to determine whether adjuvant tamoxifen treatment for breast cancer is associated with reduced contralateral (opposite side) breast cancer risk for BRCA1 and/or BRCA2 mutation carriers. (Adjuvant is a therapy added to other treatments for a disease.) Many breast cancer patients have tumors that have estrogen receptors. These tumors grow and spread when exposed to estrogen. Women with these hormone-responsive cancers are typically prescribed tamoxifen, which blocks estrogen and reduces their risk of cancer recurrence by 40%; however, women with breast cancer who have BRCA1 or BRCA2 gene mutations are not typically offered tamoxifen treatment.
The researchers reviewed data from observational data, self-reported at enrollment and at follow-up from the International BRCA1, and BRCA2 Carrier Cohort Study, Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer, and Breast Cancer Family Registry. Eligible women were BRCA1 and BRCA2 mutation carriers who had been diagnosed with unilateral (on-sided) BC since 1970; these women had no other cancers or had used tamoxifen before they were diagnosed with breast cancer. Statistical analyses were conducted to determine whether tamoxifen reduced the risk of recurrent cancer in the contralateral breast.
Of 1,583 BRCA1 and 881 BRCA2 mutation carriers, 383 (24%) BRCA1 and 454 (52% BRCA2 carriers) took tamoxifen after their first breast cancer diagnosis. The researchers found 520 contralateral breast cancers over 20,104 person-years of observation. The reesearchers found that 24% of the BRCA1 carriers and 52% of the BRCA2 carriers began taking tamoxifen after being diagnosed. During an average of eight years of follow-up, 520 women, 24% of the BRCA1 carriers and 17% of the BRCA2 carriers, developed cancer in the contralateral breast.
Women with the BRCA1 mutation were 62% less likely to develop a second cancer if they took tamoxifen, while BRCA2 carriers had a 67% lower risk with the drug. Tamoxifen was linked to fewer second cancers whether or not women's original tumors had been estrogen-receptor positive.
This authors concluded that their study provides evidence that tamoxifen use is associated with a reduction in contralateral breast cancer risk for BRCA1 and BRCA2 mutation carriers. They recommend that further follow-up of these women will provide increased statistical power for future prospective (forward-looking) analyses.