[Diminished expression of CD5 and/or CD7 surface antigens as the first clue of diagnosis for monoclonal T lymphocytosis].

The significance of precursor status for mature T-cell neoplasms has not been elucidated. Diagnosis of T-cell neoplasms is often challenging and sometimes overlooked when leukocytosis is not evident and neoplastic cell morphology is hardly distinguishable. Here, we report two cases of monoclonal T lymphocytosis (MTL) without evident lymphocytosis and lymphadenopathies that show slightly diminished CD5 and/or CD7 surface antigens as the first clue of diagnosis. Recently, some reports have demonstrated the possibility that monoclonal lymphocytosis precedes leukemia/lymphoma. Although its clinical significance is unknown, flow cytometric analysis of peripheral blood is useful for detection of occult MTL and careful follow-up is required.