CHECKMATE 647: A PHASE 2, OPEN‐LABEL STUDY OF NIVOLUMAB IN RELAPSED/REFRACTORY PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA OR RELAPSED/REFRACTORY PRIMARY TESTICULAR LYMPHOMA. (June 2017) - Nayak, L.; Iwamoto, F.M.; Ferreri, A.J.; Santoro, A.; Singer, S.; Batlevi, C.; Batchelor, T.; Rubenstein, J.; Johnston, P.; Ramchandren, R.; Soussain, C.; Drappatz, J.; et al.