Immunological detection of covert leukaemic spread in mediastinal T-cell lymphoblastic lymphoma.

A double immunofluorescence assay for terminal transferase (TdT) and surface membrane T-cell differentiation markers, defined by monoclonal antibodies, was used to analyse peripheral blood and bone marrow from patients with mediastinal T-cell lymphoma with clinically localized disease. In 2 patients, at diagnosis and during two subsequent relapses, cells with abnormal immunological phenotype were detected in low numbers in the peripheral blood, which contained no morphologically abnormal cells on any occasion. Bone marrow was uninvolved by immunological criteria on 3 of 4 examinations. The findings suggest that morphologically undectable T-lymphoblasts escape from the site of disease origin in the thymus in patients with lymphoblastic lymphoma, leading to "seeding" of sites such as bone marrow and central nervous system. Furthermore, the techniques described appear to be potentially very useful for the monitoring of lymphoblastic lymphoma patients for early prediction of disease relapse.