Human Milk and Matched Serum Demonstrate Concentration of Select miRNAs.

Background: Pregnancy-associated breast cancers (PABCs), especially those diagnosed after childbirth, are often aggressive, with a poor prognosis. Factors influencing PABC are largely unknown. Micro(mi)RNAs are present in many human body fluids and shown to influence cancer development and/or growth. Subjects and Methods: In six nursing mothers, we determined if breast cancer-associated miRNAs were (1) detectable in human breast milk and (2) if detectable, their relative expression in milk fractions compared to matched serum. We evaluated by quantitative PCR the expression of 11 cancer-associatedmiRNAs (10a-5p, 16, 21, 100, 140, 145, 155, 181, 199, 205, 212) in breast milk cells, fat and supernatant (skim milk), and matched serum. Results: miRNA expression was detectable in all samples. For 10/11 miRNAs, mean relative expression compared to control (Delta Ct) values was lowest in milk cells, the exception being miR205. Relative concentration was highest in the skim fraction of milk for all miRNAs. Expression was higher in skim milk than matched serum for 7/11 miRNAs and in serum for 4/11 miRNAs. miR205 expression was higher in all milk fractions than in matched serum. Conclusion: In conclusion, the expression of breast cancer-associated miRNAs is detectable in human breast milk and serum samples. The concentration is highest in skim milk, but is also detectable in milk fat and milk cells.