Anaplastic thymic carcinoma: a clinicopathologic and immunohistochemical study of 6 cases

SummaryPrimary thymic anaplastic (“undifferentiated”) carcinoma is an unusual thymic neoplasm that, to date, has not been properly characterized. We present 6 such cases in an attempt to better define this entity. The patients were 5 women and 1 man with an age range from 42 to 72 years (mean, 62 years). None of the patients had any history or radiologic evidence of tumor elsewhere. All patients presented with symptoms related to their anterior mediastinal masses: shortness of breath, chest pain, and cough. Histologically, the lesions were characterized by infiltrative tumors with marked cytologic atypia, bizarre tumor giant cells, and atypical mitoses. None of the neoplasms showed areas of other well-defined types of thymic carcinoma. Immunohistochemically, all tumors showed positive staining for pancytokeratin, 40% expressed Pax8, and none reacted with thyroid transcription factor 1 or β-human chorionic gonadotropin. Follow-up available for 4 patients showed that 3 patients had died 14, 22, and 63 months after diagnosis, whereas 1 patient is alive 4 months after diagnosis. Two patients were lost to follow-up. Anaplastic thymic carcinoma is a distinct morphological type of thymic carcinoma with an aggressive clinical course, which needs to be included in the differential diagnosis of tumors displaying giant cells in the anterior mediastinum.