Abstract 117: Association of TGF-β2 levels in breast milk with breast biopsy diagnosis

Background: TGF-β isoforms play a dual role in breast carcinogenesis, acting at early stages as tumor-suppressors and later as tumor-promoters. TGF-β isoforms are expressed in breast tissues and secreted in milk, suggesting that analysis of levels in milk might have value for understanding the effect of pregnancy and lactation on breast carcinogenesis. Data suggest that TGF-β2 levels in milk are higher than TGF-β1, show heterogeneity among women, and may vary with psychosocial stress, maternal immunity, and length of nursing. We assessed whether TGF-β2 levels in milk from each breast were correlated with a history of prior breast biopsy (biopsied vs. not biopsied) and biopsy diagnosis. Methods: Fresh breast milk donated by lactating women who had either undergone or were scheduled for a breast biopsy was shipped on ice to a central laboratory. Breast cancer risk factors were obtained via questionnaire and biopsy diagnoses were extracted from pathology reports. Milk was processed to create cellular-enriched and cellular-depleted fractions and frozen at -20[≤]C prior to testing. TGF-β2 levels in milk were analyzed using the Quantikine Human TGF-β2 Immunoassay (R&D Systems DB250) and quantified using the Coomassie Plus (Bradford) Assay (Thermo Scientific) kits in bilateral samples donated by182 women, including duplicate samples from 1 woman (n= 366). We compared log transformed TGF-β2 (pg/ml) and TGF-β2/total protein ratio (pg/μg) levels for biopsied and non-biopsied breasts using t-tests and ordinary least squares regressions adjusted for confounders and clustering of observations by woman. Results: TGF-β2 levels ranged 0 - 68,070 pg/ml and total protein levels ranged 1,558- 36,198 μg/ml. The levels of TGF-β2 in the biopsied and non-biopsied breasts were correlated (r2 = 0.64), albeit not statistically significant. Controlling for mother's attained age, age at first birth, age of baby (surrogate for length of nursing), number of live births, time since breast biopsy, and race, did not alter the finding for TGF-β2 or the TGF-β2/total protein ratio. But, mean levels of TGF-β2 proteins were highest in milk among women with cancer (9971 pg/ml, n=16), followed by proliferative lesions with atypia (8842 pg/ml; n=4) biopsy diagnoses. TGF-β2 levels were lower among women with non-proliferative biopsy diagnoses (4131 pg/ml; n=292) as compared with those who had proliferative lesions with atypia or cancer (P