Thymic epithelial neoplasms with Rhabdomyomatous component: a Clinicopathological and Immunohistochemical study of 7 cases.

Seven primary thymic epithelial neoplasms, three thymomas, and four thymic carcinomas with rhabdomyomatous component are herein described. The patients are two women and 5 men between the ages of 42 and 62years (average: 52years). Clinically, the patients presented with non-specific symptoms of cough, chest pain, and dyspnea. None of the patients had history of myasthenia gravis or of previous malignancy. Diagnostic imaging revealed the presence of an anterior mediastinal mass in all the patients. Surgical resection was accomplished in all the cases. The three thymoma cases were encapsulated tumors: histologically two were lymphocyte rich (WHO type B1) and one was an atypical thymoma (WHO type B3). All the thymic carcinomas were ill-defined tumor masses with infiltrative borders and histologically were high grade carcinomas. In each tumor, in different proportion, there were easily identifiable areas with rhabdomyomatous component characterized by larger cells with eosinophilic cytoplasm and eccentrically placed nuclei. Immunohistochemical stains in all cases showed clearly demarcated presence of the epithelial component (keratin positive / desmin and myoglobin negative) and the rhabdomyomatous component (desmin and myoglobin positive / keratin negative). The three patients with thymoma are alive and without recurrence 3 and 5years after surgical resection, while three patients with carcinoma died between 2 and 3years post-surgical resection. One patient with thymic carcinoma was lost to follow-up. The current cases highlight the ubiquitous distribution of myoid cells in different types of thymic epithelial neoplasms.