Primary intrapulmonary thymoma. A clinicopathologic and immunohistochemical study of eight cases.

We describe eight cases of primary intrapulmonary thymoma occurring in seven women and one man between the ages of 25 and 77 years. Clinically, all patients had initial radiographic findings of a parenchymatous intrapulmonary mass without evidence of mediastinal involvement either radiologically or at surgery. The lesions varied from 0.5 to 10 cm in greatest diameter. Five tumors were located close to the hilum, while the other three were discovered deep within the lung and in subpleural locations. In one case, the lesion appeared to arise endobronchially and infiltrate the surrounding parenchyma. In another case, in addition to the main hilar mass, there were two smaller tumor nodules found deep within the same lung. Histologically, the lesions were characterized by the classic biphasic cellular composition of thymomas, i.e., an admixture in varying proportions of epithelial cells and lymphocytes. Four cases were characterized by sheets of lymphocytes admixed with scattered epithelial cells that were separated by fibrous bands into lobules. Three cases were composed predominantly of sheets of epithelial cells admixed with scattered small lymphocytes and containing prominent perivascular spaces. In two of these cases, focal areas of spindling of the cells were noted. One case was composed predominantly of a spindle cell proliferation with perivascular spaces and numerous small lymphocytes. Immunohistochemical stains for keratin and epithelial membrane antigen in six cases highlighted the epithelial cells scattered against the lymphoid cell background. Seven patients were treated by surgery. In one patient the tumor was deemed inoperable at the time of exploration owing to extensive pleural infiltration and was treated by postoperative radiation; the lesion recurred locally in the pleura 8 years later. Clinical follow-up in three patients after surgical incision showed them to ba alive and well without evidence of disease at 10 months, 2 years, and 8 years, respectively. Two of the patients had been followed clinically for 2 and 4 years following discovery of their lung masses on routine chest radiograph before resection of their tumors. Two patients died of unrelated conditions; in one of them, the lesions had been followed clinically for 6 years before surgery; this patient died 6 months later from coronary artery disease, without evidence of recurrence or metastasis. Our findings suggest that intrapulmonary thymomas are slow-growing tumors that may respond well to surgical resection when confined to the lung. As with their mediastinal counterparts, invasive tumors will require additional treatment for the possibility of recurrence of metastasis.