,15 Accordingly, clinical outcome in ara-C–treated patients with AML is negatively correlated with SAMHD1 expression levels.15, 16, 17 Contrary to AML, no clear correlation of SAMHD1 expression and ara-C responses could be identified in MCL,18,19 suggesting the existence of SAMHD1-modulating factors in MCL. The gene discussed is SAMHD1; the disease is acute myeloid leukemia.