Kensler KH, et al. - Among 3021 postmenopausal estrogen receptor-positive (ER+) breast cancer patients in the Breast International Group (BIG) trial 1–98, a four-armed, double-blind, phase III randomized clinical trial, researchers evaluated the prognostic and predictive value of androgen receptor (AR) expression. In the BIG 1–98 study, a comparison was made of 5 years of tamoxifen or letrozole monotherapy, or sequences of 2 years and 3 years treatment with one drug and then the other. Observations revealed no association of AR expression with prognosis. In addition, there was no heterogeneity of the letrozole vs tamoxifen treatment effect by AR expression. Findings suggest no significance of AR expression as an informative biomarker for the selection of adjuvant endocrine therapy for postmenopausal women with ER+ breast cancers.