Thymic carcinomas: clinicopathologic study of 37 cases from a single institution

Thymic carcinomas represent the rarest and the more aggressive form of thymic epithelial tumors. We retrospectively reviewed a series of 37 consecutive cases seen in our hospital over a 15-year period. The patient group consisted of 14 female and 23 male patients, aged 31 to 80 years (mean = 57). Nineteen patients were smokers (mean 29 PY). Two nonsmokers had undergone radiotherapy for breast cancer, respectively, 9 and 15 years earlier. Twenty-four cases were squamous cell carcinomas (SCCs) expressing CD5 (90 %) and CD117 (87 %) and displaying a c-Kit mutation (n = 3). Ten cases were atypical carcinoids, including four associated with MEN1 and three others with Cushing syndrome. Three cases were undifferentiated large cell carcinomas including one associated with a type A thymoma. Twenty-seven patients had undergone a total (n = 25) or subtotal (n = 2), often extended resection. The overall survival (OS) rate was 66.6 % at 36 months, and median OS was 94 months. Carcinoid tumors (P = 0.007), surgical resection (P = 0.009), and Masaoka-Koga stage II (P = 0.049) were significantly associated with better OS. The TNM and three-grade staging systems were also significantly associated with survival but were not superior to the Masaoka-Koga system. Mediastinal lymph node recurrences treatable by reoperation and pulmonary metastases were the most frequent events in carcinoid tumors and SCCs, respectively. In conclusion, our case series suggests that smoking and radiation might constitute previously unrecognized risk factors. It confirms that SCCs express both CD5 and CD117 and possibly a c-Kit mutation. Lymph node dissection should be systematic when resection is performed, especially for carcinoid tumors.