Primary atypical carcinoid of the parietal pleura expressing KIT

The author reports an extremely rare case of atypical carcinoid of the pleura expressing KIT. An 81-year-old Japanese man with emphysema was found to have a mass (3×3×2 cm) in the left parietal pleura by various imaging modalities. Video-assisted tumorectomy was performed, but could not excise it completely. Histologically, the tumor was composed of atypical cells arranged in trabecular, ribbon-like, and rosette patterns. Mitotic figures and necrosis were present. The tumor cells were argyrophil. Immunohistochemically, the tumor cells were positive for pancytokeratins, cytokeratin (CK) 18, chromogranin (focal), p53, KIT, and Ki67 (labeling=17%). In contrast, the tumor cells were negative for CK5/6, CK7, CK19, CK20, CK34βE12, epithelial membrane antigen, vimentin, S100-protein, α-smooth muscle actin, desmin, CEA, TTF-1, CDX-2, AFP, HepPar-1, synaptophysin, CD56, CA19-9, CD15, neuron specific enolase, serotonin, CD34, platelet-derived growth factor-α, calretinin, thrombomodulin, WT-1, B72.3, and D2-40. The pathologic diagnosis was atypical carcinoid of the pleura. The patient was examined by whole body computed tomography, magnetic resonance imaging, and positron emission tomography, but there were no tumors other than the pleural tumor. Endoscopic examinations including upper and lower gastrointestinal tract revealed no tumors. Therefore, the pleural tumor was thought to be primary. Ten months later, the patient developed metastatic lesions in the vertebular and femoral bones, and died of respiratory failure. Autopsy was not performed. To the best of the author's knowledge, there are no cases of primary carcinoid in the pleura in the English literature. This case is also interesting in that the atypical carcinoid expressed KIT.