RAC1 and T-cell non-Hodgkin lymphoma: As a class, these trivalent mutations are translocations or truncating mutants that involve the c-terminal SH3 domain, and are commonly observed in PTCL, NOS, but are quite distinct from a class of monovalent mutations that, despite eliminating Notch inhibitor capacity, preserve Rac1 and NFAT activating capacity, and are more commonly observed in alternative T-cell lymphomas (including CTCL, AITL, and ATLL).