Optimizing Tissue Adequacy for Molecular Testing in Small Biopsies for Primary Lung Neoplasms: A Root Cause Analysis and Proposed Solutions

Summary: Introduction: Lung cancer is often detected at late stages with limited treatment options. Molecular testing (MT) has emerged as an important therapeutic and prognostic tool for non-small cell lung cancer (NSCLC). The results of these tests are pivotal for guiding clinical decisions in the management of advanced NSCLC. Adequate tissue for MT is essential, as insufficient cell counts can lead to testing failure. Repeat biopsies delay the initiation of appropriate therapies, increase the risk of procedure-related injuries, and are not cost-effective. Published data show that approximately 40% of tissue biopsies obtained in primary lung neoplasms are adequate for MT – a phenomenon which was also observed at our institution. The aim of this study was to understand the root cause of insufficient pulmonary biopsy tissue for MT and propose solutions to increase adequate sampling. Materials and Methods: Within the Mayo Clinic patient database, 56 patients from 2022 who had undergone biopsies for NSCLC with MT ordered were identified. The MT protocol involved an in-house developed Next-Generation Sequencing method utilizing both cytology smears and paraffin embedded blocks. A comprehensive chart review was conducted to gather data on the biopsy methods employed, including endobronchial ultrasound (EBUS)-guided fine needle aspiration (FNA) and/or core needle biopsy (CNB), as well as the adequacy of tissue for MT. Various data points were scrutinized, including the number of needle passes, mass or lymph node size, and performance of rapid on-site evaluation (ROSE). A root cause analysis was performed using a fishbone diagram and Pareto chart (Figure 1). To validate the findings from the 2022 cohort, we developed a predictive model and assessed its performance against a cohort of 39 patients with EBUS-guided FNA/CNB in 2023, all with MT ordered (Table 1). Results: Overall, among specimens obtained by EBUS in 2022, 32.1% of NSCLC biopsies proved inadequate for MT. Notably, 73.2% of biopsies with ROSE yielded adequate tissue for MT, compared to 57.1% of specimens obtained without ROSE. Furthermore, 77.8% of patients who underwent both FNA and CNB had sufficient tissue for MT. In contrast, only 57.1% of specimens were adequate for MT when FNA smears alone were obtained, and 66.7% were adequate with CNB alone. Remarkably, when ROSE was performed alongside both FNA smears and CNB, 88.9% of patients had adequate tissue for MT (Figure 2). Transitioning to the 2023 cohort, when ROSE and both FNA and CNB were utilized, only 10.5% of cases were inadequate for MT (Table 1), demonstrating substantial agreement with the 2022 cohort (89.5% agreement). Conclusions: This study reveals that, for biopsies obtained by EBUS, the use of ROSE enhances tissue adequacy for MT. CNB of lesional tissue in addition to FNA smears significantly improves adequacy for MT. In cases where tissue availability is constrained, alternative MT methods, such as a lung cancer-targeted gene panel, could be considered, as they require half the cell counts compared to complete Next-Generation Sequencing. Communicating with clinicians about the importance of biopsy collection methods and quantity of tissue needed for MT is critical for timely initiation of therapy and decreased need for repeat biopsies.