Research Article Serum Factors and Clinical Characteristics Associated with Serum E-Screen Activity

Background: The E-Screen bioassay can measure the mitogenicity of human serum and thus may be useful as a biomarker in epidemiologic studies of breast cancer.While the assay’sMCF-7 cells are known to proliferate in response to estrogen, the specific determinants of variation in E-Screen activity in human serum samples are poorly understood. We sought to identify serum molecules and patient characteristics associated with serum E-Screen activity among postmenopausal women. Methods: Postmenopausal women (N 219) aged 55 to 70 years with no history of postmenopausal hormoneuse or breast cancer completed aquestionnaire andprovidedablood sample. Serumwas analyzed for E-Screen activity and a variety of molecules including sex hormones, growth factors, and environmental chemicals. Stepwise selection procedures were used to identify correlates of E-Screen activity. Results: Serum samples fromallwomen haddetectable E-Screen activity, with amedian estradiol equivalents value of 0.027 ng/mL and interquartile range of 0.018–0.036 ng/mL. In the final multivariable-adjusted model, serum E-Screen activity was positively associated with serum estradiol, estrone, insulin-like growth factor– binding protein (IGFBP)-3, and testosterone levels (all P < 0.05), as well as body mass index (P 0.03). Serum E-Screen activity was lower among women with higher SHBG (P < 0.0001) and progesterone levels (P 0.03). Conclusion: Serum E-Screen activity varies according to levels of endogenous estrogens and other serum molecules. Obesity appears to confer additional serum mitogenicity beyond its impact on the measured hormones and growth factors. Impact: By capturing mitogenicity due to a variety of patient and serum factors, the E-Screen may provide advantages for use as a biomarker in breast cancer studies. Cancer Epidemiol Biomarkers Prev; 22(5); 962–71. 2013 AACR