Thymic epithelial neoplasms with rhabdomyomatous component: a clinicopathological and immunohistochemical study of 7 cases

Seven primary thymic epithelial neoplasms, 3 thymomas and 4 thymic carcinomas, with rhabdomyomatous component are herein described. The patients are 2 women and 5 men between the ages of 42 and 62 years (average, 52 years). Clinically, the patients presented with nonspecific 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 3 thymoma cases were encapsulated tumors: histologically, 2 were lymphocyte rich (World Health Organization type B1), and 1 was an atypical thymoma (World Health Organization 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 3 patients with thymoma are alive and without recurrence 3 and 5 years after surgical resection, whereas 3 patients with carcinoma died between 2 and 3 years after 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.