Analytical Validation of the Oncotype DX Genomic Diagnostic Test for Recurrence Prognosis and Therapeutic Response Prediction in Node-Negative, Estrogen Receptor–Positive Breast Cancer

BACKGROUND: Oncotype DX is a clinically validated, high-complexity, multianalyte reverse transcription-PCR genomic test that predicts the likelihood of breast cancer recurrence in early-stage, node-negative, estrogen receptor-positive breast cancer. The Recurrence Score (RS) provides a more accurate, reproducible measure of breast cancer aggressiveness and therapeutic responsiveness than standard measures. Individualized patient management requires strict performance criteria for clinical laboratory tests. We therefore investigated the analytical performance of the assay. METHODS: Assays used a pooled RNA sample from fixed paraffin-embedded tissues to evaluate the analytical performance of a 21-gene panel with respect to amplification efficiency, precision, linearity, and dynamic range, as well as limits of detection and quantification. Performance variables were estimated from assays carried out with sample dilutions. In addition, individual patient samples were used to test the optimized assay for reproducibility and sources of imprecision. RESULTS: Assay results defined acceptable operational performance ranges, including an estimated maximum deviation from linearity of <1 cycle threshold (C(T)) units over a > or =2000-fold range of RNA concentrations, with a mean quantification bias of 0.3% and CVs of 3.2%-5.7%. An analysis of study design showed that assay imprecision contributed by instrument, operator, reagent, and day-to-day baseline variation was low, with SDs of <0.5 C(T). CONCLUSION: The analytical and operational performance specifications defined for the Oncotype DX assay allow the reporting of quantitative RS values for individual patients with an SD within 2 RS units on a 100-unit scale.