Background and objective <p>As the use of real-world evidence (RWE) expands, evaluating whether Japanese real-world data (RWD) can reproduce clinical trial findings is crucial. This study aimed to determine whether pseudonymized medical information collected under the Next-Generation Medical Infrastructure Act could reconstruct a patient cohort comparable to the Japanese subgroup of the OAK trial and to evaluate progression-free survival (PFS) and overall survival (OS) in patients with non-small cell lung cancer (NSCLC) treated with atezolizumab.</p> Methods <p>We conducted a historical cohort study using the Millennium Medical Record database. Medical information collected between 1 October 2015, and 31 October 2022 was utilized, and the study itself was conducted from September 2023 to February 2024. Patients treated with atezolizumab for NSCLC were identified, and eligibility criteria from the OAK trial were applied. Effectiveness outcomes were extracted from unstructured electronic medical record text by trained abstractors through manual review of the medical records, ensuring robustness of the assessments.</p> Results <p>A total of 75 patients were analyzed. The median PFS was 3.5 months (95% CI 2.3–8.9), comparable to the 4.2 months (95% CI 2.8–4.4) reported in the OAK trial’s Japanese subgroup. Subgroup analyses showed numerical distance, with shorter PFS in patients with advanced stage and poor performance status, consistent with clinical expectations. Median OS was not reached, likely due to censoring from untracked hospital transfers.</p> Conclusions <p>This study demonstrated the feasibility of extracting PFS from unstructured text in RWD, yielding results comparable to clinical trials. While OS estimation faced challenges due to tracking limitations, future integration with the National Database under the revised law is expected to enhance accuracy, paving the way for using this infrastructure to generate external control arms.</p>