8535 Background: Next generation sequencing (NGS) is an important emerging tool in precision oncology, allowing identification of a growing number of clinically validated and investigational therapeutic molecular targets. A potential limitation is that some NGS assays require more DNA input than more limited molecular assays. Endobronchial ultrasound fine-needle aspiration (EBUS-FNA) is a minimally invasive procedure for sampling mediastinal and pulmonary lesions, but it is unknown if it provides adequate material for NGS. Methods: An IRB approved, retrospective review was performed of patients undergoing EBUS-FNA by thoracic surgeons at our institution 3/1/14 - 9/28/16. NGS was performed using an assay developed at our institution that detects mutations in up to 410 genes (MSK-IMPACT). Samples diagnostic for malignancy and with MSK-IMPACT requested were identified. Pathology and clinical data were drawn from the medical record and MSK-IMPACT results were examined. Results: 784 EBUS-FNA were done in the study period. MSK-IMPACT was requested on 115 positive samples. MSK-IMPACT was successful in 99 samples (86.1%), identifying an average of 12.7 mutations at a mean coverage depth of 806X. In 17 (17.2%) samples, tumor content was suboptimal ( < 20% of nucleated cells), with fewer identified mutations than in cases with higher tumor content (6.8 vs 13.9, p = 0.01). NGS was performed on paraffin-embedded cell blocks in 93 cases (93.9%), and in 6 cases DNA extraction was performed from residual cytological material isolated from supernatant including cell-free DNA. Failures were attributable to low cell content (7), high contamination by benign cells (4) or both (1) and processing issues (4). No difference in surgical or radiologic parameters were identified for failed or suboptimal samples. Conclusions: In our practice, EBUS-FNA has a high rate of success for obtaining adequate tissue for NGS. Ability to utilize cell-free DNA for molecular studies – a new process in our lab – allows increased success of molecular testing in scant samples. Further studies may identify factors contributing to NGS failure and to improving success for samples with minimal cellularity.
Next-generation sequencing-based multi-gene mutation profiling of solid tumors using fine needle aspiration samples: promises and challenges for routine clinical diagnostics
