Felty Syndrome–Associated Clonal Cytotoxic T‐Cell Disease With Terminal Aggressive Progression: Shared STAT3 and TET2 Mutations Across a Prolonged Disease Course

ABSTRACT Introduction Biological overlap between Felty syndrome (FS) and clonal cytotoxic T‐cell disorders is increasingly recognized, but aggressive progression is uncommon. Methods We investigated an autopsy‐confirmed case of terminal aggressive clonal T‐cell disease that developed after a 4‐year clinical course diagnosed as FS using serial immunophenotypic and molecular analyses. Results Evolving γδ T‐cell populations, TCR clonality, shared STAT3 and TET2 mutations, and a newly emergent complex karyotype supported clonal continuity and terminal aggressive progression. Conclusion This case provides clinicopathological evidence of long‐term evolution in FS‐associated clonal cytotoxic T‐cell disease. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission