Originally published as JCO Early Release 10.1200/JCO.2006.10.5023 on May 29 2007

This Article Full Text Full Text (PDF) Erratum (v25,p4862) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Save to my personal folders Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wu, A. H. Articles by Doerge, D. R. Search for Related Content PubMed PubMed Citation Articles by Wu, A. H. Articles by Doerge, D. R.

Tamoxifen, Soy, and Lifestyle Factors in Asian American Women With Breast Cancer

Anna H. Wu, Malcolm C. Pike, Lee D. Williams, Darcy Spicer, Chiu-Chen Tseng, Mona I. Churchwell, Daniel R. Doerge

From the Departments of Preventive Medicine and Medicine, University of Southern California Keck School of Medicine, Los Angeles, CA; and the National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR

Address reprint requests to Anna Wu, PhD, Health Sciences Campus, Department of Preventive Medicine, University of Southern California, Los Angeles, CA 90033; e-mail: annawu{at}usc.edu

Purpose: 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.

Patients and 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 premenopaual 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.

Conclusion: 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.

published online ahead of print at www.jco.org on May 29, 2007.

Supported by grants from the Susan G. Komen Foundation (POP02-1896), the California Breast Cancer Research Program (9PB-0089), and the National Institute of Environmental Health Services (5P30 E207048). Incident breast cancer cases for this study were collected by the USC Cancer Surveillance Program (CSP), which is supported under subcontract by the California Department of Health. CSP is also part of the National Cancer Institute's Division of Cancer Prevention and Control Surveillance, Epidemiology, and End Results Program, under contract number N01CN25403. D.R.D. is supported in part by the National Institute on Aging (P01-AG024387) with additional support from the National Institute for Complementary and Alternative Medicine, Office of Dietary Supplements, and the Women's Health Initiative.

The views presented in this article do not necessarily reflect those of the US Food and Drug Administration.

Authors’ disclosures of potential conflicts of interest and author contributions are found at the end of this article.