Defining ctDNA Metrics in Posttransplant Lymphoproliferative Disorder (PTLD)

The purpose of this study is to find out if there is a benefit to giving rituximab with etoposide, prednisone, vincristine, cyclophosphamide and doxorubicin (R-EPOCH) in participants who have high-risk B-cell PTLD in their 2nd phase of treatment (consolidation) while those with low-risk disease will be spared of chemotherapy and treated with rituximab consolidation alone. This study is also being done to find out about the usefulness of circulating tumor DNA (ctDNA), a novel blood test which, has been shown to help guide treatment decisions in other types of lymphoma. The goal is to answer the question if ctDNA is a viable and informative tool in treating PTLD with the hope that in the future it may be used to individualize study treatment for participants with PTLD in a way that limits study treatment toxicity without losing the effectiveness of the treatment plan.