Tamoxifen, soy, and lifestyle factors in Asian American women with breast cancer.
OBJECTIVE
Soy foods have been a staple in Asia for centuries but the consumption of this food in the West is recent. Intake of soy among women at high risk for or with breast cancer has become a public health concern because genistein, a major component of soy, has weak estrogenic effects on breast epithelium, and has been found to negate the benefit of tamoxifen in some animal and in vitro studies.


METHODS
We conducted a cross-sectional study in Asian Americans with breast cancer who were tamoxifen users (n = 380) to investigate the association between soy intake and circulating levels of tamoxifen and its metabolites (N-desmethyl tamoxifen [N-DMT], 4-hydroxytamoxifen [4-OHT], and 4-hydroxy-N-desmethyl-tamoxifen [endoxifen]).


RESULTS
Serum levels of tamoxifen or its metabolites were unrelated to self-reported intake of soy or serum levels of isoflavones. Blood levels of tamoxifen were 81% higher in postmenopausal women age 65 or older compared with premenopausal women age 45 or younger (P = .005); similar patterns of results were observed for the tamoxifen metabolites. Levels of N-DMT were 27% (P = .03) lower among women in the highest tertile of body mass index (BMI, > 24.4 kg/m2) compared with those in the lowest category (BMI 21.5). Women who used hypertensive medications had higher levels of tamoxifen (P = .02) and N-DMT (P = .04) compared with nonusers.


CONCLUSIONS
We found no evidence that soy intake adversely affected levels of tamoxifen or its metabolites. However, age, menopausal status, BMI, and use of hypertensive medications significantly influenced circulating levels of tamoxifen and its metabolites in this population.
Wu
Anna H
AH
Department of Preventive Medicine, University of Southern California Keck School of Medicine, Los Angeles, CA 90033, USA. annawu@usc.edu
Pike
Malcolm C
MC
Williams
Lee D
LD
Spicer
Darcy
D
Tseng
Chiu-Chen
CC
Churchwell
Mona I
MI
Doerge
Daniel R
DR
D000328:Adult; D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000097:blood / Q000627:therapeutic use; D001213:Asian / Q000706:statistics & numerical data*; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000208:ethnology* / Q000401:mortality; D003430:Cross-Sectional Studies; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000378:metabolism; D008019:Life Style; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment; D030262:Soybean Proteins / Q000008:administration & dosage / Q000378:metabolism*; D016019:Survival Analysis; D013629:Tamoxifen / Q000097:blood* / Q000627:therapeutic use; D014481:United States
D018931:Antineoplastic Agents, Hormonal; D007529:Isoflavones; D030262:Soybean Proteins; D013629:Tamoxifen