Differential Expression of Cancer-Related Proteins in Paired Breast Milk Samples from Women with Breast Cancer

Background: Breast cancer risk increases during pregnancy and remains elevated for a number of years thereafter. Cancer-associated proteins that are secreted into breast milk may provide a means to detect cancer in the lactating breast or to assess future breast cancer risk. Objective: To determine whether proteins linked to breast cancer would be differentially expressed in matched (both breasts from each participant) human milk samples collected from women with unilateral breast cancer. Methods: Five cancer-associated proteins (basic fibroblast growth factor [bFGF], YKL-40, neutrophil gelatinase-associated lipocalin, and transforming growth factor beta 1 and beta 2) were analyzed in milk provided by 5 lactating women, 4 of whom were known to have cancer in 1 breast (and the opposite breast clinically disease free) at the time of milk collection and 1 who developed breast cancer 2 years after milk collection. Results: Expression was significantly higher for TGF beta 2 (P = .03) and bFGF (P = .03) in the breasts with cancer. Conclusion: These proteins may play a role in assessing a woman's risk of pregnancy-associated breast cancer. Because of variable protein concentration among patients and the limited sample size, the results are considered preliminary.