CD44 and primary central nervous system lymphoma: Methods: We used indirect immunofluorescence double staining for CD20/CXCR4, CD20/CXCR5, CD20/CXCR7 and CD20/CD44 on enucleated eyes of a PCNSL xenograft mouse model with PVRL phenotype (PCNSL group) in comparison to a secondary CNS lymphoma xenograft mouse model (SCNSL group).