Objective: To investigate the clinical, morphologic and immunophenotypic properties of the patients with small cell variant of T-cell prolymphocytic leukaemia(T-PLL).

Methods: Peripheral blood and bone marrow cytomorphologic and immunophenotypic examination, and T-cell receptor(TCR) gene rearrangement detection were used to verify the diagnosis for 2 patients with lymphocytosis. Two patients were treated with combined chemotherapeutic protocol based on fludarabine.

Results: At diagnosis of case 1, the main lymphocytes of peripheral blood smear were the small mature lymphocytes without nucleoli. The immunophenotype of the cells was CD3+CD5+CD7+CD4+CD8+TCRα/β+. The patient achieved complete remission after treatment with combined with CTX of fludarabine. The disease relapsed at 32 months after diagnosis. The abnormal lymphocytes were medium-sized ones with a visible nucleolus. Immunophenotyping showed that the leukemic cells were predominantly CD8 positive(CD3+CD5+CD7+CD4-CD8+TCRα/β+). Both the peripheral blood and bone marrow cells of case 2 were predominanthy the mature lymphocytes, and their immunophenotype was HLA-DR+CD7+CD5+CD4+CD3+CD2+CD56+cCD3+TCRα/β+. The combined fludarabine therapy was ineffective.

Conclusions: Immunophenotypical switch from CD4+CD8+ to CD4-CD8+ may be associated with a poor response to chemotherapy. CD56 expression is an independent poor prognostic factor for primary refractory disease in T-PLL and may be considered for implementing risked-adapted therapeutic strategies.