Differential expression of cancer-associated proteins in breastmilk.

Breast cancer that develops during or shortly after pregnancy is frequently more aggressive than cancer diagnosed at other times in a woman's life. To better understand the patterns of cancer-related protein expression in the breasts of lactating women, we determined the differences in total and individual protein expression in milk based on (a) three time points during lactation (early, mid, and late), (b) length of lactation, and (c) parity. Breastmilk was collected from 72 healthy lactating women within 10 days of starting lactation (transitional [T]), 2 months after lactation started, and during breast weaning (W). Sixteen proteins whose expression is altered in breast cancer (11 kallikreins [KLKs], basic fibroblast growth factor [bFGF], YKL-40, neutrophil gelatinase-associated lipocalin, and transforming growth factor [TGF] beta 1 and beta 2) were evaluated. The concentration of total milk protein decreased over time (p < 0.01 at 2 months and W compared with T). After we controlled for total protein, KLK6 and TGF beta 2 significantly increased, and bFGF decreased from T to W. Neither length of nursing nor parity significantly influenced individual protein expression at the W time point. On the other hand, length of nursing did influence the difference in KLK6, -7, and -8 expression between the W and T time points. Total milk protein concentration is lower in the mid and late phases of nursing. Biomarker differences between T and W milk samples in KLK6, TGF beta 2, and bFGF are consistent with a protective effect of nursing.