Marked efficacy of rituximab in two patients with Waldenstrom macroglobulinemia-like multiple myeloma.

Abstract

e18548 Background: Rituximab (R) has been deemed to be ineffective in multiple myeloma (MM), despite CD20 expression in 10-15% of MM. Here we report two cases, selected by a genomic approach, with an excellent response to single agent R. Methods: as below Results: Patient 1: A 49 yr old male with IgG lambda MM with 80% bone marrow (BM) plasma cells (PC) and IgG level of 23 g/L had been treated elsewhere with one cycle of CRD. Here, we noted CD-2 subclass by gene expression profilin (GEP), however without spiked expression of CCND1 and CCND3 genes as manifestation of a t[11:14] or a t[6:14]. GEP further revealed a del 6q and overexpression of EBI2, both commonly seen in Waldenstrom Macroglobulinemia (WM). All findings were confirmed by FISH. Unsupervised clustering in the context of MGUS, untreated MM and WM-PC, confirmed WM-like MM in this patient. Sole therapy with R (750 mg/m2/d x 5d, weekly x 4, bi-weekly x 4 and then monthly) resulted in a reduction of IgG from 1850 mg/dL to 950 mg/dl and BM PC from 60% to 10% at 9 months and a decrease in sLFLC from 68 mg/dL to 10 mg/dL at 12 months follow up. Patient 2: Based on the above observation, we identified a second patient. This 37-yr old male had been diagnosed with lambda light chain MM 42 months earlier with a BM PC of 15%, lambda light-chain proteinuria of 1.9 g/d and sLFLC in the 200mg/dL range. Because of absence of CRAB criteria, he was followed expectantly. Rising BM PC to 50% and concern for end-organ damage motivated a detailed examination of GEP data. GEP showed high expression of CD20 and EBI2 and absence of CCND1 and CCND3 spikes. This was confirmed by FISH, which also revealed a del 6q. As in the first case, this patient co-segregated with WM. R treatment on the same schedule resulted in a reduction of sLFLC levels from 249 mg/dL to 29.9 mg/dl and of Bence Jones proteinuria from 1766 mg/d to 242 mg/d. Conclusions: The presumed lack of activity of R in MM needs to be revisited in light of the marked response noted in these 2 patients. Studies are in progress (a) to extend R therapy to similar cases, and (b) to more fully characterize the prevalence of genetic/phenotypic characteristics, as seen in these 2 cases, among several thousand MM patients. This updated information will be presented at the meeting.