IMPORTANCE: Biomarker testing for driver mutations is essential for selecting appropriate non-small cell lung cancer (NSCLC) treatment but is insufficient. OBJECTIVE: To investigate the status of biomarker testing and drug therapy for NSCLC in Japan for identifying problems in treatment. DESIGN, SETTING, AND PARTICIPANTS: The REVEAL cohort study included retrospective data collection and prospective follow-up from 29 institutions across Japan. Of 1500 patients diagnosed with advanced or recurrent NSCLC between January 1 and March 18, 2021, 1479 were eligible. Cases recognized at the wrong clinical stage (n = 12), diagnosed outside the study period (n = 6), not treated according to eligibility criteria before recurrence (n = 2), and with deficient consent acquisition procedure (n = 1) were excluded. MAIN OUTCOMES AND MEASURES: The primary end point was the biomarker testing status. Treatment-related factors were examined. RESULTS: Among the 1479 patients included in the analysis, the median age was 72 (range, 30-95) years; 1013 (68.5%) were men; 1161 (78.5%) had an Eastern Cooperative Oncology Group performance status 0 or 1; 1097 (74.2%) were current or past smokers; and 947 (64.0%) had adenocarcinoma. Biomarker status was confirmed in 1273 patients (86.1%). Multigene testing was performed in 705 cases (47.7%); single-gene testing, in 847 (57.3%); and both, in 279 (18.9%). Biomarker testing was performed for EGFR in 1245 cases (84.2%); ALK, in 1165 (78.8%); ROS1, in 1077 (72.8%); BRAF, in 803 (54.3%); and MET, in 805 (54.4%). Positivity rates among 898 adenocarcinoma cases included 305 (34.0%) for EGFR, 29 (3.2%) for ALK, 19 (2.1%) for ROS1, 11 (1.2%) for BRAF, and 14 (1.6%) for MET. Positivity rates among 375 nonadenocarcinoma cases were 14 (3.7%) for EGFR, 6 (1.6%) for ALK, 1 (0.3%) for ROS1, 3 (0.8%) for BRAF, and 8 (2.1%) for MET. Poor physical status, squamous cell carcinoma, and other comorbidities were associated with hampered multigene testing. Targeted therapy was received as first-line treatment by 263 of 278 cases (94.6%) positive for EGFR, 25 of 32 (78.1%) positive for ALK, 15 of 24 (62.5%) positive for ROS1, 9 of 12 (75.0%) positive for BRAF, and 12 of 19 (63.2%) positive for MET. Median overall survival of patients with positive findings for driver gene alteration and who received targeted therapy was 24.3 (95% CI, not reported) months; with positive findings for driver gene alteration and who did not receive targeted therapy, 15.2 (95% CI, 7.7 to not reported) months; and with negative findings for driver gene alteration, 11.0 (95% CI, 10.0-12.5) months. Multigene testing for nonadenocarcinomas and adenocarcinomas accounted for 705 (47.7%) of all NSCLC cases. CONCLUSIONS AND RELEVANCE: These findings suggest that multigene testing has not been sufficiently implemented in Japan and should be considered prospectively, even in nonadenocarcinomas, to avoid missing rare driver gene alterations.