Impact of Achieving an Early Complete Response in Multiple Myeloma and Predictors of Subsequent Outcome

Background: Achievement of a complete response (CR) to therapy in multiple myeloma (MM) early in disease course correlates with improvement in clinical outcomes, reflective of therapeutically sensitive disease biology. While depth of response is known to impact overall survival (OS) and progression-free survival (PFS), the effect of known prognostic variables at baseline including FISH risk and International Staging System (ISS) score outside of clinical trial settings is not well described. We sought to determine the impact of known prognostic variables in MM including FISH and ISS risk in the context of NDMM patients achieving a CR to therapy and to also examine additional predictors of outcome among this cohort.

Methods: A retrospective study was conducted on 1869 NDMM patients who had ≥ 2 consecutive monoclonal protein immunofixation (IFE) studies in the serum and urine available within 24 months from diagnosis. We identified the number of patients who had ≥ 2 negative serum and urine IFE as a surrogate for achieving CR (N=461), since a bone marrow biopsy is not routinely performed to confirm CR in the non-trial setting. A Kaplan-Meier model was used to compare median PFS and OS between patients achieving a CR vs. non-CR and a multivariate analysis was performed to adjust for known prognostic variables. A cox proportional hazards model was used to determine the prognostic impact of baseline FISH (high risk vs. standard risk) and ISS scores (3 vs.1 and 2) on PFS and OS, among patients achieving a CR vs. non-CR, and identify additional prognostically significant variables within the CR cohort.

Results: The median length of follow-up for the entire cohort (n=1869) was 64 months (range: 1-199). The median time from diagnosis to achievement of CR among the CR cohort was 9.8 months (0.20-23.8 months). The median PFS for CR (n=461) vs. non-CR (n=1408) patients was 42.0 vs. 29.3 months (p<.0001) and median OS was 124.4 vs. 85.6 months (p<.0001), respectively (Figure 1). The impact of achieving a CR on outcomes was retained after adjusting for FISH, ISS, age, sex, autologous stem cell transplant, and involved heavy chain as follows: PFS HR 0.57 (0.43-0.76; p=0.0001); OS HR 0.56 (0.43-0.74; p<0.0001). The baseline FISH and ISS risk on PFS and OS comparing CR vs. non-CR patients are shown in Table 1, with both variables having statistically insignificant impact on PFS and OS among the CR cohort. We examined several variables present at baseline and at the time of CR to determine their impact on PFS and OS, including age, sex, and non-IgG involved heavy chain (baseline), and thrombocytopenia (<150,000), hypoalbuminemia (<3.5 g/dL), and immunoparesis (at time of CR). The following variables were found as inferior predictors on PFS within the CR cohort with hazard ratios as follows: male gender, HR 1.36 (1.05-1.75; p=0.02) and non-IgG involved heavy chain, HR 2.2 (1.55-3.2).The following variables were found as predictors for inferior outcomes on OS within the CR cohort with hazard ratios as follows: Age> 75 years, HR 2.7 (1.54-4.8; p=.0005); male gender, HR 1.5 (1.1-2.02; p=.008); serum albumin <3.5, HR 1.54 (1.1-2.08; p=.004); and non-IgG involved heavy chain, HR 1.75 (1.23-2.47; p=.002). On multivariate analysis, age, hypoalbuminemia, and non-IgG involved heavy chain retained prognostic significance for OS.

Conclusion: Attainment of an early CR in NDMM confers improvement in PFS and OS. Our study confirms these findings and suggests that achievement of CR neutralizes the impact of baseline FISH and ISS risk on PFS and OS. Among the CR cohort, age> 75 years, male sex, non-IgG involved heavy chain, and hypoalbuminemia at the time of CR predict for inferior overall survival.

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