title: Risk of late-stage breast cancer after a childbirth.
abstract: A pregnancy may lead to hormone-induced growth of breast tumors. The authors investigated whether women in the first years after childbirth had a higher incidence of breast cancer and, in particular, a higher incidence of late-stage tumors (i.e., a large tumor, nodal involvement, or histologic grading II + III). The study was based on a population-based cohort of 1.5 million Danish women born between 1935 and 1978. Between 1978 and 1994, 10,790 incident cases of breast cancer were identified in a nationwide cancer registry. Overall, uniparous and biparous mothers experienced a transient increased risk that did not appear to be attributable to delayed cancer diagnosis. The risk of being diagnosed with a tumor whose diameter was larger than 5 cm was, on average, 53% higher during the first 10 years after birth compared with later. The risk of tumors of less than 2 cm was not significantly associated with time since the latest birth. In conclusion, after a childbirth, mothers experience a transient increased risk of breast cancer and, in particular, a relatively high risk of late-stage disease. This finding suggests that pregnancy-related factors transiently induce a high growth rate in cells that are already malignant and stimulate new tumor growth.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Wohlfahrt
authors.forename: P K
authors.initials: PK
authors.lastname: Andersen
authors.forename: H T
authors.initials: HT
authors.lastname: Mouridsen
authors.forename: M
authors.initials: M
authors.lastname: Melbye
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D007743:Labor, Obstetric; D008875:Middle Aged; D011247:Pregnancy; D012042:Registries; D012306:Risk; D013997:Time Factors