A Case of Lung Typical Carcinoid in a Patient with Spontaneous Regression Who Showed Peripheral Eosinophilia and Eosinophilic Pleural Effusion

━━ Background. Lung typical carcinoids with spontaneous regression or paraneoplastic syndromes other than carcinoid syndromes are relatively rare. Case. A 69-year-old man was found to have a chest abnormal-ity during a medical checkup. Chest computed tomography (CT) showed nodules in the right S 5 and 8/9th inter-costal space and a mass in the right parietal pleura, near the 9-10th thoracic spine. The paravertebral mass re-gressed on chest CT, but right pleural effusion appeared three months later. He was transferred to our hospital and found to have peripheral eosinophilia and eosinophilic pleural effusion. A CT-guided biopsy was performed, as chest CT showed an increase in the size of the nodule at the right chest wall. However, the diagnosis was difficult due to an insufficient sample volume, and thoracoscopic partial lung resection with pleural tumor resection was performed. The histopathological samples showed tumor cells that were positive for neuroendocrine markers. The cell division was extremely low, and the patient was diagnosed with lung typical carcinoid (pT1cN0M1a pStage IVA). After resection, the peripheral eosinophilia improved spontaneously, and the right pleural effusion did not relapse. Despite the advanced stage, the target lesion was resected, and careful follow-up is being con-ducted. Conclusion. We experienced a very rare case of a patient with lung typical carcinoid with spontaneous regression and paraneoplastic syndromes.