DELTA-T-LYMPHOCYTOSIS IN A PATIENT WITH THYMOMA

Background. Malignant thymoma is composed of neoplastic epithelial cel ls and small lymphocytes. Rarely, patients also may have peripheral T- lymphocytosis. These lymphocytes have been considered nonneoplastic be cause of their microscopic appearance and immunophenotype, as well as gene rearrangement studies. Methods. A 42-year-old man developed lymph ocytosis 3 years after the completion of intensive combined chemoradio therapy protocol for lymphocytic thymoma. These peripheral blood lymph ocytes were evaluated phenotypically and genotypically. Results. Immun ophenotyping established that the cells were CD3 positive, CD4 negativ e, CD8 negative, T-cell receptor (TCR)-alpha/beta negative, and TCR-ga mma/delta positive. Gene rearrangement studies with TCR-delta probe co nfirmed the monoclonality of these cells. Chromosome analysis showed d eletion of chromosome Y. The clinical course was progressive and had t he features of malignant lymphoma. Conclusions. To the authors' knowle dge, this is the first report of a patient with thymoma in whom monocl onal proliferation of T-gamma/delta peripheral blood lymphocytes was c onfirmed immunophenotypically and genotypically. These monoclonal TCR- gamma/delta lymphocytes may belong to the malignant clone of the thymo ma; however, the possibility that they represent an evolution of a sec ond lymphatic malignancy cannot be excluded.