Collaborative Group on Hormonal Factors in Breast Cancer2021-12-142022-03-182021-12-142022-03-1819960010-7824https://repositorio.sibdi.ucr.ac.cr/handle/123456789/17443The Collaborative Group on Hormonal Factors in Breast Cancer has brought together and reanalysed the worldwide epidemiological evidence on breast cancer risk and use of hormonal contraceptives. Original data from 54 studies, representing about 90% o f the information available on the topic, were collected, checked and analysed centrally. The 54 studies were performed in 26 countries and include a total o f 53,297 women with breast cancer and 100,239 women without breast cancer. The studies were varied in their design, setting and timing. Most information came from case-control studies with controls chosen from the general population; most women resided in Europe or North America and most cancers were diagnosed during the 1980s. Overall 41% o f the women with breast cancer and 40% of the women without breast cancer had used oral contraceptives at some time; the median age at first use was 26 years, the median duration o f use was 3 years, the median year o f first use was 1968, the median time since first use was 16 years, and the median time since last use was 9 years. The main findings, summarised elsewhere,1 are that there is a small increase in the risk o f having breast cancer diagnosed in current users o f combined oral contraceptives and in women who had stopped use in the past 10 years but that there is no evidence o f an increase in the risk more than 10 years after stopping use. In addition, the cancers diagnosed in women who had used oral contraceptivestended to be less advanced clinically than the cancers diagnosed in women who had not used them.engCANCERENFERMEDADESANTICONCEPTIVOSArticle