Addiction of primary cutaneous gamma-delta T-cell lymphomas to JAK-STAT signaling

Primary cutaneous gammadelta T-cell lymphoma (PCGDTL) is a mature T-cell lymphoma (TCL) of the skin with a median survival of 31 months and no effective therapies. PCGDTLs frequently possess mutations in the JAK/STAT pathway, including in JAK1, JAK3, STAT3, STAT5B, and SOCS1. We hypothesized that single-agent JAK inhibition may be effective in PCGDTLs, particularly those with targetable JAK/STAT pathway mutations. Herein, we demonstrate the near-complete response of two PCGDTL cases to single-agent JAK inhibitors, ruxolitinib or cerdulatinib. However, both patients eventually relapsed with acquired mutations in JAK1, JAK3, or STAT5B.