Thymic carcinoma associated with multilocular thymic cyst: a clinicopathologic study of 7 cases.

We present 7 cases of thymic carcinoma associated with a multilocular thymic cyst (MTC). The patients were 5 men and 2 women aged 22 to 71 years (mean, 49.3 y). Clinically, 6 patients presented with chest, sternal, or upper extremity pain, and in 1 patient the tumor was an incidental finding. Grossly, 4 tumors were described as multilobulated solid-cystic masses, whereas 3 cases were described as solid tumors with a white-yellow cut surface and areas of hemorrhage and necrosis. The tumor size ranged from 7.0 to 10.0 cm (mean, 8.1 cm). Histologically, 4 cases were classified as squamous cell carcinoma, and 1 each as sarcomatoid (spindle) cell carcinoma, papillary carcinoma, and basaloid carcinoma. In addition to the tumor component, prominent MTC changes were observed in the adjacent remnant thymic tissue. Immunohistochemical studies were conducted in 2 cases of squamous cell carcinoma. The neoplastic cells were positive for cytokeratin (CK), CK5/6, and p63, and showed variable reactivity for CK7 and CD5. Clinical follow-up showed that 4 patients were alive and well, 2 to 63 months after diagnosis, and 3 patients were alive with disease, 13 to 33 months after diagnosis. This study expands the morphologic spectrum of thymic carcinoma associated with MTC, detects a higher incidence than previously believed, and highlights the importance of adequate sampling and proper evaluation of all cystic lesions of the anterior mediastinum so as not to mistake malignancy for a benign cystic process.