Autologous Stem Cell Transplantation Provides Additional Cytoreduction Following Induction Therapy in Multiple Myeloma.

Background: High dose therapy (HDT) and stem cell transplant has been shown to improve survival in patients with myeloma and remains the standard of care. However, the reported results of initial HDT in these patients reflect the combined effect of the initial therapy and the HDT. The contribution of HDT on its own is often difficult to analyze in this group of patients with varying degree of response to initial therapy. In this single institution retrospective study, we have analyzed the results of HDT in a group of patients with measurable disease at the time of HDT.

Methods: We identified patients from our transplant database, who had measurable disease at the time of initiation of transplant as defined by a serum M protein of ≥ 1.0 g/dL, 24 hour urine M-protein ≥ 200 mg or a bone marrow plasma cell % of ≥ 30. Details regarding the clinical outcome were obtained from the database and from patient clinical records. Chi square test was used for comparison of nominal variables and t-test for continuous variables. Kaplan Meier analysis was used for comparing survival and Cox proportional hazards was employed to identify predictors of progression free and overall survival. Responses were defined by the EBMTR criteria, using the measurements at the time HDT and the lowest measurement obtained. VGPR required a 90% reduction in the serum M component with urine protein < 100 mg/24 hours.

Results: A total of 440 patients were studied; 271 (61.5%) of whom had a transplant within one year of their diagnosis. Among the 271 patients, 140 (52%) were in the initial plateau, 99 (36%) failed to achieve a PR to initial therapy and 32 (12%) were in their first relapse. Given the known differences in the outcome between these groups of patients, those receiving an early transplant were analyzed separately. The response rates included CR (24%), VGPR (7%), PR (52%), MR or less (17%) and among the late transplants CR (23%), VGPR (8%), PR (61%) and MR or less (8%). The median progression free survival was 23.6 mos and the overall survival from HDT was 62 mos. In a multivariate analysis, presence of cytogenetic abnormalities (RR: 2.5) and high plasma cell labeling index (≥ 1%) (RR: 2.4) at HDT and failure to achieve a CR or VGPR (RR: 1.7) were prognostic for decreased progression free survival post HDT. In a similar model, only high PCLI (RR: 2.8) and abnormal cytogenetics (RR: 2.5) at HDT predicted for poor overall survival after transplant.

Conclusion: This study provides a sense of the contribution of HDT, independent of the initial therapy, by determining responses based on the immediate pre-transplant disease measurements and the best values observed post transplant. In this group of patients with residual measurable disease after the initial therapy, HDT therapy leads to complete responses in nearly a quarter of the patients and a VGPR in another 7%, an outcome associated with better progressin free survival. While measurements at transplant do not correlate strictly with response to initial therapy, the aim of this study was to understand the individual contribution of HDT in these patients. Thus some of the patients who would have been classified as having a partial response to induction and HDT may be classified as non-responders in this analysis. These numbers will provide a historical comparison for trials evaluating novel consolidation therapies for myeloma.