Metastatic pulmonary tumor from type 3 gastric neuroendocrine tumor

Type 3 NETs are reported to metastasize to other organs or lymph nodes; however, there are few reports of gastric NETs causing isolated pulmonary metastasis. We report a rare case of primary gastric neuroendocrine tumors (NETs) with lung metastasis. The patient presented with multiple gastric submucosal tumors (SMTs) and a solid nodule in the S1 + 2 of the left lung. Endoscopic mucosal resection of the stomach and a left upper lobectomy of the lung were successfully performed. The histopathological findings of the gastric SMTs and lung tumor revealed type 3 gastric NETs and a metastatic pulmonary tumor, although TTF-1 is positive in the stomach and the lung. In this time, we reported a rare case of a metastatic pulmonary tumor from gastric type 3 NETs. In addition, we also realized the limitations of immunohistochemistry in identifying the site of origin for NETs and the need to rely on morphologic and clinical features.