The intrauterine origin of male breast cancer: a birth order study in Denmark. Sorensen, H T 1; Olsen, M L 1; Mellemkjaer, L 2; Lagiou, P 3; Olsen, J H 2; Olsen, J 4 Abstract: First pregnancies are known to have higher oestrogen levels than later ones and first-born women are at increased breast cancer risk compared with later-born women. We hypothesized that a birth order effect might be even more evident in male breast cancer patients, in whom oestrogens in adult life are generally low. In a population-based study in Denmark involving 77 male breast cancer patients and 288 population controls, first-born men compared with later-born men had a relative risk of 1.71 for the disease (95% confidence interval (CI) 1.00-2.92). This result is in line with that seen in female breast cancer cases and indicates that male breast cancer may have roots in the intrauterine life, oestrogens being a likely mediator European Journal of Cancer Prevention. 14(2):185-186, April 2005. Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.