Chromophobe-like carcinoma of the thymus: A clinicopathological and immunohistochemical correlation of 5 cases.

Five cases of primary thymic carcinoma with distinct histopathological features resembling chromophobe carcinomas are presented. The patients were four men and one woman ranging in age between 43 and 72 years. Clinically, the patients presented with non-specific symptoms of dyspnea and chest pain. Diagnostic imaging revealed the presence of anterior mediastinal masses. All patients underwent complete surgical resection of their tumors via thoracotomy. Grossly, the tumors measured between 4.0 and 5.5 cm in greatest diameter and were ill-defined neoplasms with infiltrative borders; they were light brown in color and had a lobulated surface. Areas of hemorrhage and necrosis were not identified. Histologically, all tumors shared similar histopathological features, mainly the presence of infiltrative tumor islands separated by a fibrocollagenous stroma. At higher magnification, the neoplastic cellular proliferation was composed of medium-sized, round to polygonal cells with eosinophilic or granular cytoplasm and a clear perinuclear cytoplasmic halo, which imparted a chromophobe-like appearance. Nuclear atypia and mitotic activity were identified. Histochemical stains for colloidal iron were negative while immunohistochemical stains for pancytokeratin, cytokeratin 5/6, and p40 were positive in all cases, supporting squamous differentiation in these tumors. Clinical follow-up information was obtained in three patients all of whom died between 3 and 5 years after initial diagnosis, while two patients were lost to follow-up. The cellular characteristics of these tumors represent an unusual variant of thymic carcinoma that may pose a diagnostic challenge in small biopsies and that could be easily confused with other primary or metastatic tumors.