DLI are an efficient treatment for CML in relapse after allogeneic stem cell transplantation, with 60 to 70% of complete response. However, major side effects such has graft-versus-host disease (GVHD) or pancytopenia are frequently observed after this treatment. Imatinib mesylate has also been shown to be effective in a such situation (Blood 2002, 100 (5): 1590–95). In the present study, we report the French experience, with a 3 years median follow-up of 26 patients in relapse of CML after allograft (21 sibling, 4 unrelated, 1 cord blood transplantations). At time of treatment with IM, twenty patients were in chronic phase and 5 only were in molecular relapse, while 4 patients were in blastic phase. Median time from graft to relapse was 36 months (3–132 months) and the median time from relapse to Imatinib was 15 months ( 1–96 months). Ten patients had already received DLI, 14 patients Interferon. Only 6 patients had no treatment prior to IM. With a median follow-up of 32 months (16–44 months), 19 patients are alive and 5 died. The majority of patients in chronic (19/20) phase are alive. At time of last follow-up : Three (11%) patients fail to respond to IM, 2 (8%) have a partial response, 12 (46%) are in CCR with 9/12 in molecular remission, and 4 (15%) patients present relapse (1 blastic phase, 3 molecular relapse). Eleven patients are evaluable for VNTR chimerism, 8(72%) achieved full donor chimerism at last follow-up. IM was well tolerated, and 2 GVHD reactivations were observed but 8 (42%) patients experienced cytopenias requiring drug modulation or withdrawal, and two grade IV toxicities (muscle cramps, cardiomyopathy). Six patients stopped IM (2 toxicities, 4 long term molecular remissions). Four of these patients experienced molecular relapse (3 after 12 months, 1 at 3 months). One patient achieved molecular remission after a new challenge with IM. In conclusion, Imatinib mesylate is efficient and safe treatment for CML in relapse after allogeneic HSCT without reactivating GVHD, and is able to restore full donor chimerism in a majority of responsive patients. A complete and sustained molecular response is obtained in about one third of patients, however molecular relapse is frequent after IM withdrawal. The place of IM and/or DLI for CML in relapse after allogeneic HSCT needs to be addressed prospectively and requires a randomized trail.

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