DNA ploidy assessment of breast milk (colostrum) in primiparous women of different ages

Recent studies on breast cancer risk factors suggest that nursing may have a protective effect. The mechanism behind this is unknown. To investigate whether removal of tumorigenic epithelial cells in breast milk contributes to the reduced risk of developing breast cancer, DNA ploidy of cells in colostrum breast milk from 200 primiparous women was studied with flow cytometry. No woman displayed an abnormal DNA content of the shed epithelium in the milk. Although it cannot be excluded that tumor cells with a near-diploid DNA content are present, our results suggest that early shedding of a large clone of transformed aneuploid epithelium is not a common event and that the protective effect of nursing on breast cancer risk is due to other mechanisms, e.g., hormonal changes in the breast.