Maintenance therapies are intriguing for PCNS with a gents that cross the blood brain barrier. Much early work is being done. There are several studies involving rituximab or lenalidomide or temazolamide, but there have notbeen randomized studies and no guidelines, NCCN including have recommended maintenance therapies.
Batchelor T, Lesser G, Grossman S, et al. Rituximab monotherapy for relapsed or refractory primary central nervous system lymphoma. Proceedings from the 2008 annual meeting of the American Society of Clinical Oncology. Abstract #2043.
Niels Murawski, Michael Pfreundschuh et al, Rituximab maintenance therapy in central nervous system lymphoma?Leukemia & Lymphoma Volume 50, 2009 - Issue 10
NCCN, PCNSL 2017
james L. Rubenstein, Eleanor Fraser, Paul Formaker, James Chi-Chiang Lee, Nianhang Chen, Mallory Kock, Wesley Cheung, Xiaomin Wang, Pamela N. Munster, Bertil Damato et al, J Clin oncol 2016 (suppl; abstr 7502)