Risk of contralateral breast cancer after tamoxifen use among Danish women
Menée au Danemark auprès de 15 863 cas et 21 670 témoins, cette étude évalue l'association entre un traitement par tamoxifène et le risque de cancer du sein controlatéral
Purpose : Tamoxifen reduces the risk of contralateral breast cancer (CBC), but little is known about the long-term risk. Methods : From the database under the Danish Breast Cancer Cooperative Group (DBCG), we identified 15,863 users and 21,670 non-users of tamoxifen among women diagnosed with breast cancer during 1977-2007. Information on CBC was obtained from the Danish Cancer Registry and the DBCG database. Cox regression analyses were carried out with estimation of hazard ratios (HR) of CBC. We also estimated HRs of current and past use of tamoxifen in each of these subsets. Results : Current use of tamoxifen was associated with reduced HRs of CBC independently of menopausal status and calendar-period. The HRs associated with past use of tamoxifen, however, varied among postmenopausal users from 1.50 (95% CI = 1.20-1.87) among users in 1977-89 to 0.87 (95%CI = 0.70-1.06) and 1.05 (95%CI =0.68-1.63) among users in 1990-98 and 1999-2007, respectively. No excesses or deficits of CBC were found 10 or more years since last use in postmenopausal women in any calendar-period. Conclusions : Our study confirms that tamoxifen protects against CBC while being treated. The effect of tamoxifen after cessation of treatment was not clear due to inconsistency in results by calendar-period.