A Study of Circulating Tumor DNA (ctDNA) Testing for People With B-Cell Lymphoma

The purpose of this study is to find out how many people with B-cell lymphoma who are at high risk for central nervous system/CNS relapse test positive for cerebral spinal fluid/CSF ctDNA but test negative for CNS involvement using standard tests. The study will also look at how often CNS relapse happens in people with and without detected CSF ctDNA.