CYP1B1 and breast cancer: These data, together with the observation of a higher proportion of the CYP1B1 (Val) allele among postmenopausal women with hormone receptor positive breast cancer [4], and of an association between Nigerian premenopausal breast cancer and the CYP1B1 (Leu) allele suggest that breast cancer in sub-Saharan African populations may have a different etiopathogenesis than in Caucasian or Asian populations.