Prognostic value of DNA flow cytometry in thymomas and thymic carcinomas

Thymomas are the most common anterior mediastinal masses. Malignant potential and prognosis are unrelated to histologic appearance. Deoxyribonucleic acid (DNA) flow cytometry is of prognostic significance in a variety of tumors. We reviewed the records of 35 patients who on pathologic examination had a thymoma or thymic carcinoma. Flow cytometric studies, including DNA indices (ploidy) and S phase fraction, were done on paraffin block specimens from 31 patients. We believe this is the first report of DNA flow cytometric studies in thymic pathology. Mean survival was 63.5 +/- 13.3 months for patients with benign thymomas, 10.5 +/- 4.6 months for patients with malignant thymomas, and 19.3 +/- 4.1 months for patients with thymic carcinomas. Patients with benign thymomas lived significantly longer than those with malignant thymomas (P = .001) and thymic carcinomas (P = .03). DNA flow cytometry demonstrated four aneuploid tumors (two benign thymomas and two malignant thymomas). All thymic carcinomas were diploid. There was no statistically significant difference among the groups. The mean S phase fraction was 15.22% for benign thymomas, 11.15% for malignant thymomas, and 14.31% for thymic carcinomas. No statistically significant difference was found among the groups. We conclude that flow cytometry is not a useful guide to malignant potential or prognosis in thymomas and thymic carcinomas.