Pre-diagnosis and early post-diagnosis dietary soy isoflavone intake and survival outcomes: A prospective cohort study of early stage breast cancer survivors

• Does the intake of soy food, rich in isoflavones, affect the prognostic outcomes of breast cancer (BC) survivors?

• This prospective cohort study among 1460 early-stage BC survivors revealed that pre-diagnosis soy intake was associated with a significantly 66% reduced risk of all-cause mortality, and 64% reduced risk of BC-specific mortality during the four-year follow-up since diagnosis.

• A similar risk reduction pattern was also noted for early post-diagnosis soy isoflavone intake with the respective risk reductions of 64% and 51% for all-cause and BC-specific mortality. We also observed a lower risk of recurrence in association with moderate level of soy isoflavone intake.

• Our findings provided an important evidence that soy intake is associated with more favorable prognostic outcomes among early-stage BC survivors.

Abstract

Background

There is concern that the estrogen-like effects of soy isoflavones may stimulate mammary tumor growth and interfere with the efficacy of breast cancer treatment. This study aimed to examine prospectively the associations of dietary soy isoflavone intake with all-cause mortality and breast cancer (BC) specific mortality and recurrence among BC survivors.

Design

The study included 1460 Chinese women with early-stage incident BC. Pre-diagnosis and early post-diagnosis soy food intakes were assessed at study entry, and at 18-month follow-up using validated soy food frequency questionnaire. Associations of soy isoflavone intake with prognostic outcomes within 48 months were examined using multivariable adjusted Cox proportional hazards models.

Results

We observed increasing pre-diagnosis and early post-diagnosis soy isoflavone intakes up to the third quartile (Q3) were associated with reductions for adverse prognostic outcomes. Relative to the lowest quartile (Q1), the hazard ratios (HRs) for all-cause mortality for pre-diagnosis and post-diagnosis Q3 intake were respectively 0.34 (95% CI, 0.16–0.74), and 0.44 (95% CI, 0.22–0.89). A similar risk reduction was observed for pre- and post-diagnosis intakes and BC-specific mortality when comparing Q3 versus Q1 with the respective HRs 0.36 (95% CI, 0.16–0.82), and 0.49 (95% CI, 0.23–1.01). Subgroup analyses showed more favourable prognostic outcomes in association with moderate soy intake among premenopausal women, those with triple negative cancer and recipients of tamoxifen treatment.

Conclusion

Moderate soy isoflavone intake was associated with favourable prognostic outcomes in Chinese early stage BC survivors.