describes the characteristics of 1954 female breast cancer survivors enrolled in the LACE Study who completed a soy FFQ, stratified by levels of daidzein intake. Levels of soy intake differed significantly by age at diagnosis (P < .0001), ethnicity (P < .0001), education (P < .0001), tamoxifen use at baseline (P = .005), menopausal status at diagnosis (P < .0001) and smoking status (P = .0003). There appeared to be a clear inverse relationship between soy consumption and age within each category of soy intake. Women in the oldest age category consumed the least amount of soy: 32% of women aged 70 years and older had no soy intake compared to 17% of women less than 50 years old. There were more Asian women in the ‘medium’ and ‘high’ soy intake category than women of any other ethnicity: 75% and 16% of Asians had ‘medium’ and ‘high’ soy intake compared to 32% and 4% in non-Hispanic White women. About 7% of the college graduates had high soy intake compared to only 3% women with less than or equal to a high school education. Premenopausal women were more likely to have medium or high soy intakes (53%) compared to postmenopausal women (33 %). About 10% of the non-smokers (never and past smokers) had ‘high’ soy intake compared to less than 1% of current smokers. The mean (SD) of daidzein and genistein intakes in the LACE cohort were 1.7 (4.9) and 2.4 (7.0) milligrams per day, respectively, and were highly collinear (r = 0.997, data not shown). The most frequently consumed soy foods in the LACE cohort were soy sauce, breakfast and diet shakes and drinks, tofu, diet bars, and soy protein isolate powder ().
Soy intake among members of the LACE cohort who reported consumptiona (n = 1255)
describes the effect of soy intake on breast cancer recurrence among all women and also stratified by menopausal status. Overall, there was a non-significant decreasing risk of breast cancer recurrence with increasing intakes of both daidzein (P = .20 for trend) and glycetin (P = .10 for trend). The relationship was most apparent among postmenopausal women where tests for linear trend were borderline significant for daidzein (P = .08) and glycetin (P = .06).
Multivariable delayed entry cox-proportional hazards models describing soy isoflavone intake and breast cancer recurrence, stratified by menopausal status
presents the effect of isoflavone intake on breast cancer recurrence, stratified by hormone receptor status and by tamoxifen use. The risk of recurrence according to intake of glycetin (P = .04 for interaction) varied significantly by hormone receptor type (ER− and PR− vs. ER+ or PR+), yet no evidence of interaction was apparent for intakes of daidzein and genistein (P > 0.20). Similarly, when stratified by tamoxifen use, a significant interaction between tamoxifen use and the effect of glycetin on breast cancer recurrence was observed (P = .03 for interaction). Women who used tamoxifen had a significant decreased risk of breast cancer recurrence with increasing intake of glycetin (P = .05 for trend) and a suggestive, but non-significant relationship for intakes of daidzein (P = .10 for trend) and genistein (P = .13 for trend). Women in the highest categories of daidzein and genistein intakes had an approximately 50% reduction in breast cancer recurrence that was not significant (HR for the 95th percentile of daidzein intake, 0.48; 95% CI, 0.19–1.21; HR for the 95th percentile of genistein intake, 0.48; 95% CI, 0.19–1.22). No apparent potential benefit for women who had never used tamoxifen was observed. In contrast, while there was no evidence of a trend across levels of soy intake, women who had never used tamoxifen and were in the 95th percentile of isoflavone intake had a borderline significant increased risk of breast cancer recurrence (HR for the 95th percentile of daidzein intake, 2.40; 95% CI, 0.93–6.18; HR for the 95th percentile of genistein intake, 2.42; 95% CI, 0.95–6.21).
Multivariable delayed entry cox-proportional hazards models describing soy isoflavone intake and breast cancer recurrence, stratified by hormone receptor status and tamoxifen usea
Since increasing daidzein intake was associated with a marginally decreased risk of breast cancer recurrence in both postmenopausal women and in women who had ever used tamoxifen, we examined postmenopausal women who were ever treated with tamoxifen (n = 970) and estimated the distribution of time to breast cancer recurrence, by levels of daidzein intake (‘low’, ‘medium’, and ‘high’), adjusted for soy supplement use, BMI one year prior to diagnosis, tobacco pack-years, tumor stage, age at diagnosis, race, and total energy intake (). The ‘low’, ‘medium’, and ‘high’ categories correspond to 0–7.6, 7.7–1452.9, and ≥1453 µg/day daidzein intake. After a mean follow-up time of 6.3 years from entry into the cohort, the proportion of women who recurred was inversely related to daidzein intake and was significantly lower in the highest category of daidzein intake compared to those in the lowest category (HR, 0.41; 95% CI, 0.21–0.79, P = .008 for highest versus lowest intake; P = .006 for trend).
Breast cancer recurrence among postmenopausal women using Tamoxifen, according to daidzein intake