━━ Objective. A second opinion has potential advantages of leading to the appropriate diagnosis and treatment plan for patients with cancer and medical oncologist. However, whether or not the second opinion influences the diagnosis and treatment policy of patients with thoracic malignancies remains unclear. Methods. We retrospectively investigated patients with thoracic malignancies who asked for a second opinion at the National Cancer Center Hospital in 2019. Results. A total of 540 patients asked for a second opinion, including 341 (63.1%) patients with non-small-cell lung cancer, 38 (7.0%) patients with small-cell lung cancer, 68 (12.6%) patients with thymic epithelial tumor, 16 (3.0%) patients with pleural mesothelioma, and 77 (14.3%) patients with other thoracic malignancies. Different treatment advice from that received at the referring hospital was received by 147 (27.2%) patients at the second opinion. The details concerning the proposed treatment policies included a change in the chemotherapy regimen in 51 (34.7%) patients, a change to best supportive care (BSC) in 28 (19.0%) patients, a change from BSC to chemotherapy in 24 (16.3%) patients, and a change to surgery in 12 (8.2%) patients. Conclusion. The second opinion can result in different treatment advice, including curable treatments, such as surgery, for patients with thoracic malignancies.