Background. Epidemiologic studies support the hypothesis that soy foods protect against breast cancer, in particular among Asian populations with high intake. A previous report that observed an increase in the number of women with hyperplasic epithelial cells after consuming soy raised concerns that isoflavones in soy may elevate breast cancer risk due to their estrogen-like structure. We examined the effect of a high-soy diet on the presence of epithelial cells in nipple aspirate fluid (NAF), a non-invasive method to obtain breast fluid and cells.

Methods. In a crossover design, 82 premenopausal women completed a randomized intervention with a high-soy diet of 2 servings/day and a low-soy diet with <3 servings/week for 6 months each separated by a 1-month washout period. Adherence to the intervention strategy was excellent as assessed by urinary isoflavonoid excretion and by 7 unannounced 24-hour dietary recalls. NAF samples were obtained at baseline, after 6 months, and after 13 months. Papanicolaou-stained cytology slides were evaluated in women with sufficient NAF and classified as inadequate (<10) mammary epithelial cells (class I), benign mammary epithelial cells (class II), atypical mammary epithelial cells (class III), and malignant cells present (class IV). Mixed models were applied to examine the effect of the high-soy diet on epithelial cytology as compared to baseline and the low-soy diet.Results. The mean NAF volumes for women with and without cytology specimens differed significantly; they were 58±49 vs. 19±16 μL at baseline, 59±37 vs. 13±14 μL at the end of the high-soy diet period, and 51±40 vs. 10±9 μL at the end of the low-soy diet period. At baseline, 33 women produced sufficient NAF for cytological evaluation, 36 women at the end of the high-soy diet, and 24 women at the end of the low-soy diet. For 22 (67%) participants, no change in cytological class was seen at the end of the high-soy diet and for 12 (57%) at the end of the low-soy diet, but a decrease from baseline to the end of the high-soy diet occurred in 8 (24%) and an increase in 3 (9%) women. In comparison, a decrease in 3 (14%) and an increase in 6 (29%) women was seen at the end of the low-soy diet. Although not statistically significant (p=0.05), the high-soy diet was associated with a trend in lower cytological class. Conclusions. Contrary to an earlier report, the number of NAF samples with hyperplastic epithelial cells did not increase after an intervention with soy foods in amounts consumed by Asians.

Citation Format: Gertraud Maskarinec, Shana Suzuki, Yukiko Morimoto, Ian Pagano, Adrian A. Franke, Hormoz Ehya. Cytology in nipple aspirate fluid during a randomized soy food intervention among premenopausal women. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2524. doi:10.1158/1538-7445.AM2013-2524