T-LGLL harboring a STAT5b mutation and being CD3+, CD8+, CD56+, CD16– and CD57– shows a more aggressive course with poor prognosis, whereas expression of CD4 and CD56 antigens as well as CD56, CD3, Tγδ-LGLL are often associated with a more indolent course (11, 27). This evidence concerns the gene B3GAT1 and T-cell large granular lymphocyte leukemia.