Flow cytometry in the diagnosis of mediastinal tumors with emphasis on differentiating thymocytes from precursor...

Flow cytometry (FC) has become the routine technique in the evaluation of hematopoietic neoplasms. Since the anterior mediastinum is a frequent site of involvement by both primary and secondary lymphoma/leukemia, flow cytometry plays an important role in the evaluation of mediastinal masses. The present study reviews 100 flow cytometry cases from patients presenting with mediastinal lesions. In 5 cases (5%) flow cytometry was not diagnostic due to either insufficient cell yield or low viability. In the remaining cases (95/100) cell suspensions were adequate for flow cytometry evaluation. Results showed that in 31/32 (96.8%), 2/3 (66.7%), 7/9 (77.8%), 7/8 (87.5%) and 11/11 (100%) cases of B-cell lymphoma, T-cell lymphoma, carcinoma, T-ALL/LBL and thymoma/thymic hyperplasia, respectively, the diagnosis could be reached by flow cytometry alone. Excluding HL, the general sensitivity of FC in diagnosing mediastinal tumors was approximately 92%. Among the 100 cases, flow cytometry gave non-informative results in 3 cases of diffuse large B-cell lymphoma, 1 case of peripheral T-cell lymphoma, and 3 cases of carcinoma. No false positive results were encountered. The phenotypic pattern, especially surface CD3 expression versus forward scatter, reliably discriminated between immature thymocytes from thymoma/thymic hyperplasia from T-ALL/LBL. Flow methodology has the advantage of rapid turn-around time as well as high sensitivity, enabling patients with large anterior mediastinal masses and/or superior vena cava syndrome to begin treatment as promptly as possible. In experienced hands, flow cytometry plays a valuable and complementary role to histology and immunohistochemistry in diagnosing mediastinal tumors.