Risk of Late-stage Breast Cancer after a Childbirth
Jan Wohlfahrt1, Per Kragh Andersen1,2, Henning T. Mouridsen3 and Mads Melbye1
1 Department of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark.
2 Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
3 Danish Breast Cancer Cooperative Group, Rigshospitalet, Copenhagen, Denmark.
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.
American Journal of Epidemiology Vol. 153, No. 11 : 1079-1084
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