Exploratory analysis of intensified conditioning as first line treatment for patients with high risk multiple myeloma.

Multiple myeloma has extremely heterogeneous outcomes. Among prognostic factors, t(4;14) and del(17p) are rare oncogenic events associated with very poor prognosis. In an exploratory case-control study, we compared the combination of Busulfan-Melphalan or TBI-Melphalan with high dose Melphalan as a conditioning regimen in a series of 48 patients with del(17p) or t(4;14). These regimens were preceded by a Bortezomib-containing induction. Progression-free survival (PFS) was the primary endpoint whereas overall survival (OS) and complete response (CR) rate were the secondary endpoints. Twenty consecutive cases of high-risk myeloma received a reinforced conditioning regimen of Busulfan 0.8 mg/kg x4/j IV from day-6 to day-3 pre- graft (BuMel) or total body irradiation (TBI) 12 Gy (TbiMel), having received Melphalan 140 mg/m2 at day-2 pre-graft. These cases were matched to 28 controls treated with Melphalan 200 mg/m2 at day-2 (Mel200). After intensification ± consolidation, with a median follow-up of 6.3 years, the CR rate was higher in the BuMel/TbiMel group (65% vs 50%, P = .006). No differences were observed between both groups in terms of PFS and OS (P = .96). PFS in patients with a del(17p) mutation tended to be superior in the BuMel/TbiMel group. Our exploratory study shows that reinforcing the intensification regimen with Busulfan or TBI does not seem to improve the prognosis associated to t(4;14) and del(17p) abnormalities.