Is the international staging system superior to the Durie-Salmon staging system? A comparison in multiple myeloma patients undergoing autologous transplant

The International staging system (ISS) for multiple myeloma (MM) is a validated alternative to the Durie Salmon staging system (DSS) for predicting survival at diagnosis. We compared these staging systems for predicting outcomes after upfront autologous stem cell transplantation by analyzing the outcomes of 729 patients between 1995 and 2002. With a median follow-up of 56 months the univariate probabilities (95% CI) of non-relapse mortality (NRM), relapse, progression free (PFS) and overall survival (OS) at 5 years were 7%, 68%, 25% and 52%, respectively. The median overall survival for stages I, II, III by DSS and ISS were 82, 68, 50 and 64, 68, 45 months, respectively. The concordance between the two staging systems was only 36%. Staging systems were formally compared using Cox models fit with DSS and ISS stages. Relative risks of PFS and OS were significantly different for stages I vs. II and II vs. III for DSS but only for stages II vs. III for ISS. Although both systems were predictive of PFS and OS; the DSS was superior in formal statistical comparison using Brier Score. However, neither system was strongly predictive of outcomes indicating the need for newer schemes incorporating other prognostic markers.