WEDNESDAY, Feb. 8 (HealthDay News) — Mixed soy isoflavone supplements given over a six-month period show no significant effect in reducing the proliferation of breast cancer epithelial cells in healthy women, according to a study published in the February issue of Cancer Prevention Research.

Seema A. Khan, M.D., of the Robert H. Lurie Comprehensive Cancer Center in Chicago, and colleagues conducted a randomized double-blind trial of 98 women who had more than 4,000 breast cancer epithelial cells identified by fine needle aspiration biopsy. Participants were allocated to receive soy isoflavones or placebo. Ki-67 labeling index and atypia were assessed.

The researchers found that the median Ki-67 labeling index was 1.18 at intervention and 1.12 after six months for women in the soy isoflavone group, compared with 0.97 and 0.92, respectively, in the placebo group (P for between-group change = 0.32). For menopausal women, there were no differences between the groups, but premenopausal women in the soy group had a significant increase in the Ki-67 labeling index, from 1.71 to 2.18 (P = 0.04). There was no treatment effect on cytologic atypia or nipple aspiration fluid parameters.

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“A six-month intervention of mixed soy isoflavones in healthy, high-risk adult Western women did not reduce breast epithelial proliferation, suggesting a lack of efficacy for breast cancer prevention and a possible adverse effect in premenopausal women,” the authors write.

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