Pigmented thymic carcinoids: A clinicopathological and immunohistochemicalstudy of two cases

Two cases of pigmented thymic carcinoids are presented. The patients were t wo men, 32 and 47 years of age. The two patients were asymptomatic and the tumor was discovered on routine chest radiographic evaluation. The tumors w ere treated by surgical excision in both patients. Grossly, they presented as tan-white tumors without evidence of necrosis or hemorrhage or any visib le pigmentation. Histologically, the tumors were characterized by a monoton ous proliferation of tumor cells arranged in a trabecular or nesting patter n. The tumor cells showed moderate amounts of pale eosinophilic cytoplasm, round to oval nuclei, and inconspicuous nucleoli. Mitotic activity varied f rom three to eight per 10 high-power fields. In addition, both tumors showe d prominent areas of intra- and extracellular dark pigment deposition. The pigment reacted positively with the Fontana-Masson stain and was negative f or iron stain. Immunohistochemical studies performed in one case showed imm unoreactivity of the tumor cells for chromogranin, Leu 7, and keratin. Syna ptophysin and P53 immunostains were negative. Clinical follow-up was obtain ed in one patient who was alive and well 10 years after surgical resection, The presence of abundant melanin pigment in thymic carcinoids highlights a n important pitfall for diagnosis in these tumors that should be taken into consideration in the evaluation of anterior mediastinal lesions.