━━ Objective. The clinical usefulness of the Lung Cancer Compact Panel (Compact Panel), a new multiplex next-generation sequencing test for detecting lung cancer gene mutations was prospectively evaluated. Study design. From June 2021 to December 2022, 58 cytological specimens obtained from 57 patients with suspected lung cancer by bronchoscopy, CT-guided needle aspiration biopsy, pleural or pericardial effusion puncture, and other biopsy procedures were tested using the Compact Panel, while formalin-fixed and paraffinembedded (FFPE) samples were simultaneously examined using a gene panel test, including the Oncomine Dx Target Test (ODxTT) or the AmoyDx Ⓡ Pan Lung Cancer PCR Panel Test (Amoy T). Results. With the exception of two non-lung cancer patients, 54 of 56 cytological specimens were successfully analyzed by the Compact Panel, while only 40 FFPE samples were practically tested due to different reasons (e. g. , technical failures, insufficient samples, and other reasons). Among 40 materials for which both tests were available, 36 showed consistent findings. Interestingly, four cytological specimens from four patients showed gene mutations that were only detected by the Compact Panel, and after confirming gene mutation by other companion diagnostics, the two patients underwent appropriate treatment with molecular targeted therapy. Conclusion. In clinical practice, the Compact Panel using cytological specimens was useful for detecting gene mutations in lung cancer patients.