MacGregor, C.A., Canney, P.A., Patterson, G., McDonald, R., & Paul, J. (2005). A randomised double-blind controlled trial of oral soy supplements versus placebo for treatment of menopausal symptoms in patients with early breast cancer. European Journal of Cancer, 41, 708–714.

The study looked at soy supplements versus placebo for treatment of menopausal symptoms in participants with early breast cancer and hot flashes.

Participants were randomized to receive either two soy capsules or two identical placebo capsules twice daily for 12 weeks in a double-blind fashion. The soy capsules each contained 235 mg of soy extract with 17.5 mg of isoflavones. Total dose of isoflavones was 70 mg/day. 

Seventy-two (72) participants with early breast cancer and hot flashes were randomized to 12 weeks of treatment with soy capsules or with placebo. To be considered a worthwhile treatment strategy, soy extract would need to benefit around half of the participants treated. Thus, 32 evaluable participants per arm were needed.  The median age was 51 years. Any concomitant medications for preexisting disease were allowed.

The randomized double-blind controlled trial was stratified for initial sweating/flushing score (< 2, p = 2); age at randomization (younger than 50 years, older than 50 years); currently having adjuvant tamoxifen or after ovarian suppression (yes or no).

QOL and menopausal symptoms scores were assessed at baseline and weeks 4, 8, and 12. A four-question menopausal scale was developed for the study to assess control of menopausal symptoms measured by combined estimates of severity of sweats (day or night) and flushes.

There was no significant difference in menopausal symptoms between the placebo and soy capsule arms of the study.Toxicity was mild and primarily gastrointestinal. There was no significant difference in toxicity between the 2 arms.