Introduction: Soy intake is associated with lower breast cancer risk in observational studies of Asian women, but clinical trials of soy isoflavone (ISF) supplements report no effect on biomarkers of breast cancer risk among Caucasian women. To date, there are no such trials among Asian women living in Asia. We conducted a three-armed, randomized controlled trial (RCT) to assess the effects of one-year intervention of soy isoflavone supplements (100mg/day) or soy isoflavones through diet (50mg/day) on mammographic density (MD) change among peri- and postmenopausal Malaysian women. Methodology: Healthy women between 45-65 years old were enrolled between November 2018 and December 2019 at a private tertiary hospital in Malaysia. Women were randomly assigned into the 100mg/day ISF Supplement arm, 50mg/day ISF Diet arm, or Control arm. Dense area was assessed from digital mammograms conducted at enrolment and after 12 months. We compared absolute and relative change in dense area over the study period by study arm using Kruskal Wallis tests. Results: Of the 118 women who received the intervention, 91 women completed the study whilst 27 women (23%) were lost to follow up. After 12 months of intervention, women in the ISF Supplement arm observed a marginally larger decline in dense area (-1.3cm2), compared to women in the ISF Diet arm (-0.5cm2) and Control arm (-0.8cm2), but this difference was not statistically significant (p=0.479). Notably, these effects appear to be stronger and limited to women who enrolled within 5 years of menopause, where up to 6cm2 decline in MD was observed in the ISF Supplement arm, compared to < 1.0cm in the Control arm (p=0.131). Conclusion: This RCT demonstrates a possible causal association between soy ISF intake and lower breast cancer risk among Asian women, specifically around the time of menopause, but these findings will require confirmation in a larger trial.
Citation Format: Nadia Rajaram, Beverley Yap, Mikael Eriksson, Shivaani Mariapun, Lee Mei Tan, Hamizah Saat, Evelyn Ho, Nur Aishah Mohd Taib, Geok Lin Khor, Cheng Har Yip, Weang Kee Ho, Per Hall, Soo Hwang Teo. A randomized controlled trial of soy isoflavone intake on mammographic density among Malaysian women [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-06-02.
