KMT2D (MLL2) is mutated in 30%‐80% of patients with DLBCL and FL.96, 103, 106 KMT2D is a catalytic component of the COMPASS complex, which induces transcriptional activation through H3K4me1/2 at gene enhancers. The gene discussed is KMT2D; the disease is diffuse large B-cell lymphoma.