Validation of Immunohistochemical Assays for Integral Biomarkers in the NCI-MATCH EAY131 Clinical Trial

Biomarkers that guide therapy selection are gaining unprecedented importance as targeted therapy options increase in scope and complexity. In conjunction with high-throughput molecular techniques, therapy-guiding biomarker assays based upon immunohistochemistry (IHC) have a critical role in cancer care in that they inform about the presence of a protein target. Here, we describe the validation procedures for four clinically available IHC biomarker assays - PTEN, RB, MLH1 and MSH2 - for use as integral biomarkers in the nationwide NCI-MATCH (Molecular Analysis for Therapy Choice) EAY131 clinical trial. Validation procedures were developed through an iterative process based on collective experience and adaptation of broad guidelines from the United State Food and Drug Administration (FDA). The steps included primary antibody selection, assay optimization, development of assay interpretation criteria incorporating biological considerations and expected staining patterns, including indeterminate results, orthogonal validation, and tissue validation. Following assay lockdown, patient samples and cell lines were used for analytical and clinical validation. The assays were then approved as laboratory developed tests and used for clinical trial decisions for treatment selection. Calculations of sensitivity and specificity were undertaken using various definitions of gold standard references, and external validation was required for the PTEN IHC assay. In conclusion, validation of IHC biomarker assays critical for guiding therapy in clinical trials is feasible using comprehensive pre-analytical, analytical and post-analytical steps. Implementation of standardized guidelines provides a useful framework for validating IHC biomarker assays that allow for reproducibility across institutions for routine clinical use.

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