Parity and breast cancer: confirmed evidence of an effect on age at diagnosis.

An evaluation is made of the hypothesis of Woods et al. (1) that the number of full-term pregnancies constitutes a factor of growth acceleration in breast cancer. Our results confirm, at least in part, the effect of parity on age at diagnosis of breast cancer. Patients with two or more children were significantly younger at the time of diagnosis than were those with none or one child. Age at first birth and duration of lactation do not seem to be, in this analysis, confounding factors for the observed association.