However, the effusion in this case was leaking fluid, and no evidence of malignancy was found by pathological immunohistochemistry; in previous case reports of PEL, rituximab was not effective because PEL does not express B-cell antigen.[7,8] In this case, the bone marrow pathology indicated CD20+, and rituximab had a better effect. This evidence concerns the gene MS4A1 and primary effusion lymphoma.