Analysis of a single-institution cohort of patients with Felty's syndrome and T-cell large granular lymphocytic leukemia in the setting of rheumatoid arthritis

T-cell large granular lymphocytic leukemia (T-LGLL) is a lymphoproliferative disorder characterized by a persistent increase in the number of large granular lymphocytes (LGLs), neutropenia, and splenomegaly. Clinical manifestations of T-LGLL in the setting of rheumatoid arthritis (RA) are often identical to those in which one would suspect Felty's syndrome (FS). These disorders are distinguished by the presence of T-cell clonality, which is present in T-LGLL but not in FS. Mutations in the signal transducer and activator of transcription 3 (STAT3) and 5b (STAT5b) genes can be used as molecular markers of T-LGLL, but their prevalence in FS is unknown. Eighty-one patients with RA and unexplained neutropenia or/and an increase in the number of LGLs above 2 × 10(9)/L were stratified into RA-associated T-LGLL (N = 56) or FS (N = 25) groups based on the presence or absence of T-cell clonality. STAT3 and STAT5b gene mutations were assessed in each group by means of allele-specific polymerase chain reaction assays. Clinical, immunological, laboratory data and the results of immunophenotyping of blood and bone marrow lymphocytes were also evaluated. Mutations of the STAT3 gene and an increase in the number of LGLs above 2 × 10(9)/L were detected in RA-associated T-LGLL, but not in FS (39% vs 0% and 21% vs 0%, respectively). Mutations in the STAT5b gene were not observed in either group. Expression of CD57, CD16, and CD5(−/dim) on CD3(+)CD8(+) T-lymphocytes was observed in both RA-associated T-LGLL and FS. STAT3 gene mutations or LGL counts over 2 × 10(9)/L in RA patients are indicative of T-LGLL. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00296-020-04757-4.