This open‐label, multicenter study (NCT03010982) evaluated the absolute bioavailability, characterized the disposition and metabolism, and investigated the metabolic profile of tazemetostat, a US Food and Drug Administration–approved inhibitor of enhancer of zeste homolog 2, following intravenous and oral [14C]‐labeled and unlabeled tazemetostat in patients with B‐cell lymphomas or advanced solid tumors. Here, EZH2 is linked to B-cell non-Hodgkin lymphoma.