Prolonged lactation and endometrial cancer

Background. The risk of Endometrial cancer is related to oestrogen leves, showing an increased risk with increasing endogenous or exogenous oestrogen stimulation and a reduced risk when oestrogen is opposed by progesterone. During breastfeeding may possibly redution of endogenous oestrongen oestrongen exposure is large than that of progesterone, suggesting that breastfeeding may possibly reduce the risk of endometrial cancer.Methods. The relationshiop between lactation and endometrial cancer was assessed in data from six countries, including four developing countries, that were collected for a mulinational hospital-based case-control study conducted between 1979 and 1988. In all, 136 cases were compared with 933 controls matched on age, hospital, and year of interview. Standardized questionnaires, administered in the local language, ascertained information on the lenght of time breastfed, age started and stopped breastfeeding, reproductive and cantracetive practical, and other risk factors for endometrical cancer. Conditional logistic regression was used to control for the confounding effects of gravidity and age at menarche.Results. Significant decreasing trends in risk were observed with increasing duration fo lactation, and with months of breastfeeding per pregnancy. Risk was lowest in women who had most recently lactated, and the apparrent protective effect declined with time since cessation fo breastfeeding, so that there ws no evidence for a protective effect after age 55 even in womn who had breastfed for over 5 years.Conclusions. The long-term lactation that takes place in developing countries probably reduce the risk of endometnal cancer, but this effect may not persist into ages at which this disease in most comman.