EP300 and diffuse large B-cell lymphoma: We also observed the essentiality of EP300 in several DLBCL cell lines harbouring mutation or copy number loss in CREBBP. Our results confirmed and extended the previous finding on synthetic lethal interaction between the two important epigenetic modulators, and suggest that the dependency of the remaining HAT function is a druggable vulnerability in CREBBP- or EP300-deficient DLBCLs.