T-LGL is a rare disease (accounts for 2 to 5% of chronic lymphoproliferative disorders), indolent and often asymptomatic, and mainly characterized by cytopenias (primarily neutropenia, predisposing to infections). T-LGL leukemia patients may present with recurrent bacterial infections owing to (severe) neutropenia, anemia, and hepatosplenomegaly, but one-third of patients appear to be asymptomatic at diagnosis. T-LGL arrives from expansions of effectors T-cells, CD45RA+/CD28(-)/CD27(-)/CD94+/ – with variable expression of CD57, usually TCD8+ TCR Alpha/Beta. It is important to distinguish T-LGL from reactive LGL proliferation, which is frequent, particularly in the context of viral infections, autoimmune diseases, after splenectomy or in posttransplant patients. Diagnosis of LGL leukemia is based on two mandatory criteria which help to differentiate it from reactive LGL lymphocytosis: cytological identification of lymphocytes with granules >500 cells/mm3 observed at least over 6 months, and proof of clonality.

Female patient, 64 years old, leukocytosis, lymphocytosis and B-CLL suspicion, Peripheral blood sample with white blood count 35,500 cells - marked (93%) T Double-positive proliferation.

Flow Cytometry: 93% Double-positive CD4++ CD8+ CD3++ CD2++ CD5++ CD7-/+ CD27(-) CD45RA+ TCR Alpha/Beta+ TCRCBeta1+100% (monoclonal); dim expression of CD56 and CD57; Negative expression: CD25, CD26, CD27, CD28, CD45RO, CD94, CCR7, TCL1, TCR Gamma-Delta (Figure 1).

in the analyzed smear, predominance of atypical medium-sized lymphoid cells was observed, with a globose nucleus, generally eccentric, with poorly condensed chromatin with an outline of a nucleolus, and a moderately basophilic, polarized and granular cytoplasm (Figure 1).