title: The intrauterine origin of male breast cancer: a birth order study in Denmark.
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.
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Ole Worms Allé 150, 8000 Aarhus C, Denmark. hts@dce.au.dk
authors.forename: H T
authors.initials: HT
authors.lastname: Sørensen
authors.forename: M L
authors.initials: ML
authors.lastname: Olsen
authors.forename: L
authors.initials: L
authors.lastname: Mellemkjaer
authors.forename: P
authors.initials: P
authors.lastname: Lagiou
authors.forename: J H
authors.initials: JH
authors.lastname: Olsen
authors.forename: J
authors.initials: J
authors.lastname: Olsen
mesh_terms: D001722:Birth Order; D018567:Breast Neoplasms, Male / Q000453:epidemiology / Q000209:etiology*; D016022:Case-Control Studies; D003718:Denmark / Q000453:epidemiology; D004967:Estrogens / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012307:Risk Factors
chemical_list: D004967:Estrogens