Feasibility of epidermal growth factor receptor and Kirsten rat sarcoma viral oncogene homolog mutation testing in non-plasma body fluids with low tumor cellularity using Idylla®: A proof-of-concept.

OBJECTIVES: This retrospective, single-center, small-sample proof-of-concept study aims to evaluate the feasibility of detecting epidermal growth factor receptor (EGFR) and Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations in the supernatant of non-plasma biological fluids, pleural, ascitic, or pericardial effusions, using the Idylla® platform (Ct cartridges with research use only certification for plasma samples). MATERIALS AND METHODS: Ten fluids were tested with the Ct KRAS cartridge and seven with the Ct EGFR cartridge, comparing results with Idylla® testing in formalin fixed paraffin embedded (FFPE) tissue from the primary tumor. For each sample, 100 μL of supernatant was directly pipetted into the corresponding cartridge; in turbid samples, a preliminary centrifugation step (1600 g, 10 min, room temperature) was performed. RESULTS: All cases showed concordance between fluid and FFPE results. Notably, KRAS mutations were detected in two fluids with no malignant cells and in one with only scattered tumor cells, and an EGFR mutation was detected in a sample with 5% tumor cells. Specimens had been stored at 4°C for up to 3 weeks, suggesting good DNA preservation. CONCLUSION: This simple and rapid approach appears feasible in low tumor cellularity samples and could expand molecular testing to patients without accessible tissue. Validation in larger, multicenter cohorts is warranted.