Taken together, aberrant constitutive overexpression of ARTD9 may not only serve as a novel useful prognostic biomarker for poor survival of fatal high-risk relapsed/refractory DLBCL but also as a novel rational future drug target for treatment of high-risk relapsed/refractory HR- (and BCR-) subtypes of DLBCL-NOS. Here, PARP9 is linked to diffuse large B-cell lymphoma.