Pigmented neuroendocrine tumor of the lung, showing neuromelanin

A pigmented neuroendocrine tumor was discovered incidentally in a 62-year-old woman through examination by chest computed tomography. The tumor was located in the left lower lobe, S6, of the lung and was 8 mm in diameter. The preoperative percutaneous needle biopsy was interpreted as a tumor suggestive of small cell carcinoma. Histological examination of the operated lobectomy material revealed that the nodule was a neuroendocrine tumor consisting of mainly spindle-shaped cells and several pigmented cells. Electron microscopy showed several dense-core neurosecretory-type granules in tumor cells, as well as abundant, pleomorphic electron-dense granules in pigmented cells much larger in size and most consistent with lipofuscin or neuromelanin. No melanosomes or premelanosomes were identified. Considering the result of ultrastructural and histochemical studies, the pigment was considered most likely neuromelanin. Neuromelanin is found in neurons of substantia nigra and locus ceruleus, and sympathetic ganglion cells. It is rarely found in neuroendocrine tumors and we review the available reports regarding pigmented carcinoid tumor.