KMT2D and B-cell non-Hodgkin lymphoma: The KMT2D gene (also known as MLL2 or MLL4) encodes a SET domain-containing lysine methyltransferase and is one of the most frequently mutated genes in B cell lymphomas, reported as being affected in up to 30% of DLBCL and 80% of FL (Morin et al., 2011; Pasqualucci et al., 2011; Ortega-Molina et al., 2015; Zhang et al., 2015; Chapuy et al., 2018; Schmitz et al., 2018).