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Medline ® Abstract for Reference 19

of 'Hormone receptors in breast cancer: Clinical utility and guideline recommendations to improve test accuracy'

Immunohistochemistry compared to cytosol assays for determination of estrogen receptor and prediction of the long-term effect of adjuvant tamoxifen.
Khoshnoud MR, Löfdahl B, Fohlin H, Fornander T, Stål O, Skoog L, Bergh J, Nordenskjöld B
Breast Cancer Res Treat. 2011;126(2):421. Epub 2010 Oct 19.
The purpose of this study is to compare immunohistochemistry (IHC) and cytosol-based assays for determination of estrogen receptor (ER) and prediction of response to adjuvant tamoxifen treatment in postmenopausal women with early-stage invasive breast cancer. The 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 IHC at one pathology laboratory. The median follow-up was 17 years. Six hundred eighty-three patients had tumors with ER determined by both methods, 536 (78.5%) were ER-positive by cytosol assays using the cutoff level at≥0.05 fmol/μg DNA and 539 patients were ER-positive (79%) by IHC using the cutoff level at≥10% cell stained. Thirty-nine tumors (5.7%) were ER-positive by cytosol but not by IHC, whereas the opposite pattern was found for 42 cases (6.1%). Only seven tumors had stained cells between 0 and 9% byIHC. The concordance between IHC and cytosol assays was high (88%). The kappa statistic was 0.65, 95% CI 0.58-0.72. Among patients classified as ER-negative no therapeutic benefit from tamoxifen was observed. Among patients with ER-expressing tumors, tamoxifen resulted in significantly better recurrence-free survival irrespective of the method (IHC: HR, 0.53, P<0.001; cytosol: HR, 0.53, P<0.001). The effect on overall survival was not statistically significant probably due to the limited sample size. Both IHC and cytosol assay accurately predict long-term response to adjuvant tamoxifen.
Department of Oncology, Karolinska University Hospital, Karolinska Institute, Södersjukhuset, 11883, Stockholm, Sweden. Mahmoud.khoshnoud@karolinska.se