SAN FRANCISCO (EGMN) - A new gene-based biomarker assay may help to estimate prognosis and make decisions about extended endocrine therapy in women with estrogen receptor-positive early breast cancer, new data suggest.Researchers tested the biomarker, the Breast Cancer Index (BCI), among 249 women with estrogen receptor-positive early breast cancer from the MA.17 trial, in which women received 5 years of adjuvant tamoxifen therapy and, if still disease free, were then randomized to an additional...