External Quality Assessment Identifies Training Needs to Determine the Neoplastic Cell Content for Biomarker Testing

Neoplastic cell content determination is crucial for biomarker testing. It is known that interobserver variation exists, but largescale data are missing about variation in tumor delineation and cell content determination. Results were obtained from the external quality assessment program for metastatic colorectal cancer from the European Society of Pathology (N？=？5776 observations). The study included three parts: current practices were surveyed, neoplastic cell content estimations and delineations were retrieved from stained slides, and clinical reports were analyzed.