Clinical Testing for Tumor Cell-Free DNA: College of American Pathologists Proficiency Programs Reveal Practice Trends

Abstract

Context.— Clinical testing for tumor cell-free DNA (cfDNA) has evolved rapidly, but no practice guidelines exist. Objective.— To summarize cfDNA laboratory practices based on self-reporting and assess preanalytical, analytical, and postanalytical trends that may influence the quality, accuracy, and consistency of cfDNA testing. Design.— Data were derived from the College of American Pathologists cfDNA proficiency testing program submitted by 101 participating laboratories from 2018 to 2019. Results.— Most laboratories performing clinical circulating tumor DNA testing are commercial/nonhospital (71.2%; 72 of 101) and international (77.2%; 78 of 101) laboratories. Commercial laboratories had higher monthly test volumes than hospital-based laboratories (median, 36 versus 7–8) and tended to have larger gene panels (median, 50 versus 11 genes) when panel-based testing was offered. The main clinical indications include therapy selection and treatment/disease monitoring. Plasma is the most commonly accepted specimen, which is predominantly collected in cell-stabilizing tubes. Equal proportions of laboratories use next-generation sequencing (NGS) and non-NGS methods to assess key genes, including EGFR, BRAF, KRAS, NRAS, and IDH1. Most laboratories reported a lower limit of detection (LLOD) of 0.5%, variant allele frequency or less, which did not differ by method, NGS or non-NGS, except for EGFR. Sixty-five percent (17 of 26) of laboratories using the US Food and Drug Administration (FDA)-approved non-NGS EGFR assay report analytical sensitivities higher than 0.5%, as compared to 15% (16 of 104) of laboratories using an alternative NGS or non-NGS method. There is also a wider range in LLODs obtained for the FDA-approved EGFR assay than nonapproved assays. Conclusions.— These results highlight emerging practice trends and serve as a foundation to initiate future practice recommendations.