The present disclosure teaches that the proteins encoded by the BRCA1 and BRCA2 genes are found in the milk fat globule membranes from humans and cows. Therefore, BRCA1 and BRCA2 proteins can be isolated from milk produced by lactating animals. The level of expression of BRCA1 or BRCA2 can be determined by sampling the levels of BRCA1 or BRCA2 proteins found in the MFGM of lactating animals. The present invention also includes a method of determining the likelihood that a woman will develop breast cancer by measuring the amount of the BRCA1 or BRCA2 expression during lactation. The detection of expression of BRCA1 or BRCA2 can be accomplished with an antibody raised specifically against BRCA1 or BRCA2 proteins, by isolating BRCA1 or BRCA2 from the milk fat globule membranes or by detecting activity of BRCA1 or BRCA2. The level of BRCA1 or BRCA2 is compared to a reference scale of propensity for breast cancer development correlated to normally active BRCA1 or BRCA2 levels. BRCA1, BRCA2, fatty acid binding proteins and phosphorylated proteins are found in the MFGM and the MFGM can be isolated from milk and provided in a form suitable for oral consumption, i.e. a tablet or capsule of separated milk fat globule membranes, a food additive, or a fortified dairy commodity.