The anti-tumor effects induced by LEN are mediated through the modification of the target specificity of CRBN, an E3 enzyme responsible for ubiquitinating IKZF1 and IKZF3 in MM cells (7, 8), as well as casein kinase 1 alpha (CK1α) in 5q-MDS (10). The gene discussed is CRBN; the disease is myelodysplastic syndrome.