Testing for EGFR Variants in Pleural and Pericardial Effusion Cell-free DNA in Patients With Non-Small Cell Lung Cancer

IMPORTANCE Molecular testing in non-small cell lung cancer (NSCLC) is commonly limited by inadequate tumor sample. Plasma cell-free DNA (cfDNA) genotyping as a complementary test is specific but only moderately sensitive. Genotyping of cfDNA in pleural and pericardial effusion (PE-cfDNA) can further optimize molecular diagnostic yield and reduce the need for repeated biopsies. OBJECTIVE To prospectively validate droplet digital polymerase chain reaction (ddPCR) for detection of sensitizing EGFR variants and acquired Thr790Met variant (T790M) from PE-cfDNA in patients with NSCLC. DESIGN, SETTING, AND PARTICIPANTS This prospective diagnostic validation study was conducted between September 6, 2016, and January 21, 2021 at 2 major Hong Kong cancer centers. Patients with advanced NSCLC with both wild-type and variant EGFR status and exudative PE who underwent thoracocentesis or pericardiocentesis were randomly enrolled. Patients were either EGFR-tyrosine kinase inhibitor (TKI) naive (cohort 1) or EGFR-TKI treated but osimertinib naive (cohort 2). Enrolled patients underwent pleural- or pericardial-fluid and blood sampling for ddPCR EGFR testing. EGFR status results with ddPCR testing of PE-cfDNA and blood were compared with EGFR status in matched tumor biopsy or PE cell block samples. MAIN OUTCOMES AND MEASURES Specificity, sensitivity, and concordance of PE-cfDNA for detection of sensitizing EGFR variants and acquired T790M variation. RESULTS Among 171 patients (54% female) enrolled, there were 104 in cohort 1 and 67 in cohort 2. In cohort 1, 37% (38/102) were EGFR-variant positive; PE-cfDNA showed 97% sensitivity (95% CI, 92%-100%), 97% specificity (95% CI, 93%-100%), and 97% concordance (kappa = 0.94, P < .001) for the detection of sensitizing EGFR variants. It was more sensitive than plasma in detecting sensitizing EGFR variants (97% vs 74%, P < .001). In cohort 2, 38% (15 of 40) were positive for the EGFR T790M variant; PE-cfDNA showed 87% sensitivity (95% CI, 69%-100%), 60% specificity (95% CI, 41%-79%), and 70% concordance (kappa = 0.42, P = .004) for acquired T790M. The EGFR T790M variant was detected in 51% of PE-cfDNA vs 25% of PE cell block samples. CONCLUSIONS AND RELEVANCE In this diagnostic study, EGFR variants could be accurately detected from PE-cfDNA in patients with NSCLC. More EGFR T790M was detected in PE-cfDNA than in guideline-recommended PE cell block preparations. These results suggest that PE-cfDNA can complement plasma and tumor genotyping for detecting EGFR variants in patients with advanced NSCLC.

Automated summary

This study aimed to validate the accuracy of detecting EGFR variants through PE-cfDNA using liquid biopsy in NSCLC patients. The results showed that PE-cfDNA was more sensitive than plasma in detecting EGFR sensitizing mutations. For the detection of T790M mutation, PE-cfDNA had lower sensitivity but could complement other testing methods. Therefore, PE-cfDNA can be used as one of the methods for detecting EGFR mutations in NSCLC patients.