Atypical thymoma: A report of seven patients

Background Most thymic neoplasms fall under the designation of thymoma, consisting of well-differentiated epithelial cells, resembling normal thymus. At the opposite spectrum are thymic carcinomas; the cell of origin while similar is malignant. Recently a third category of thymic neoplasms, atypical thymomas, has been recognized representing thymic neoplasms manifesting atypia although without overt cytomorphologic criteria of malignancy. Methods Seven patients with a diagnosis of atypical thymoma were encountered over a 6-year period from the patient files of the cardiothoracic division of The Ohio State Medical Center. Results In all patients there was gross or light microscopic invasive disease with involvement of the capsule, phrenic nerve, diaphragm, chest wall, and lung. Surgical extirpation/de-bulking along with radiation therapy in six and chemotherapy in one led to complete disease regression. Intrathoracic recurrences developed in 4 involving lung, pleura, chest wall and diaphragm. All patients are well. Conclusions Atypical thymomas are locally aggressive tumors with a high incidence of intrathoracic recurrence; extrathoracic spread is not seen. Our study corroborates other reports that death attributable to atypical thymoma is uncommon.