Remission status defined by immunofixation vs. electrophoresis after autologous transplantation has a major impact on the outcome of multiple myelomapatients

We have retrospectively analysed 344 multiple myeloma (MM) patients (202 de novo patients) treated in a non-uniform way in whom high-dose therapy and autologous stem cell transplantation (ASCT) response was simultaneously mea sured by both electrophoresis (EP) and immunofixation (IF), Patients in com plete remission (CR) by EP were further subclassified as CR1 when IF was ne gative and CR2 when it remained positive. Partial responders (PR) were also subclassified as PR1 (very good PR, >90% reduction in M-component) or PR2 (50-90% reduction). CR1 patients showed a significantly better event-free s urvival (EFS) [35% at 5 years, 95% confidence interval (CI) 17-53, median 4 6 months] and overall survival (OS) (72% at 5 years, CI 57-86, median not r eached) compared with any other response group (univariate comparison P < 0 .00000 to P = 0.004). In contrast, comparison of CR2 with PR1 and with PR2 did not define different prognostic subgroups (median EFS 30, 30 and 26 mon ths respectively, P = 0.6: median survival 56, 44 and 42 months respectivel y, P = 0.5). The non-responding patients had the worst outcome (5-year OS 8 %, median 7 months). Multivariate analysis confirmed both the absence of di fferences among CR2, PR1 and PR2 and the highly discriminatory prognostic c apacity of a three-category classification: (i) CR1 (ii) CR2 + PR1 + PR2, a nd (iii) non-response (EFS P < 0.00000: OS P < 0.00000: both Cox models P < 0.00000). In the logistic regression analysis, the factors significantly a ssociated with failure to achieve CR1 were the use of two or more up-front chemotherapy lines, status of non-response pre-ASCT and inclusion of total body irradiation (TBI) in the preparative regimen, Tandem transplants or th e use of multiple agents (busulphan and melphalan) in the preparative regim en resulted in a higher CRI level: none of the biological factors explored influenced the possibility of achieving CR1. These results confirm that, in MM patients undergoing ASCT, achieving a negative IF identifies the patien t subset with the best prognosis; accordingly therapeutic strategies should be specifically designed to achieve negative IF.