and prediction of response to adjuvant tamoxifen treatment in postmenopausal women with early stage invasive breast cancer. Patients and methodsThe Stockholm Breast Cancer Study Group conducted a randomized trial during 1976 through 1990 comparing adjuvant tamoxifen versus control. The patients were stratified according to tumor size and lymph node status in high risk and low risk groups. In this study we evaluated 683 patients with "low risk" breast cancer (size≤30 mm, lymph node-negative) for whom ER status had been determined by both the cytosol assays and immunohistochemistry at one pathology laboratory. The median follow up was 17 years. ResultSix hundred eighty three patients had tumors with ER determined by both methods, 536 (78.5%) were ERpositive by cytosol assays using the cut off level at ≥ 0.05 fmol/µg DNA and 539 patients were ER-positive ConclusionBoth IHC and cytosol assay accurately predict long-term response to adjuvant tamoxifen.3

The results showed that the mentioned substantial differences in terms of gene expression appeared mainly to be related to endocrine sensitivity and not to metastatic potential. However, a slight advantage during the first five years for the ER positive versus ER negative patients in terms of cumulative incidence of events, suggested that ER negativity in some cases is correlated with an increased tumour growth rate.