Comprehensive evaluation of the revised international staging system in multiple myeloma patients treated with novel agents as a primary therapy

The revised International Staging System (R-ISS) has recently been developed to improve the risk stratification of multiple myeloma (MM) patients over the ISS. We assessed the R-ISS in MM patients who were treated with novel agents as a primary therapy and evaluated its discriminative power and ability to reclassify patients from the ISS. A total of 514 newly diagnosed MM patients treated with novel agents including thalidomide, bortezomib, and lenalidomide as a primary therapy were included in this retrospective analysis. With a median follow-up duration of 42.3 months (range, 40.5-44.1), the median overall survival (OS) was 61.0 months. There was a significant difference in median OS (not reached, 60.9, and 50.1 months for stages 1, 2, and 3, respectively, P<0.001) among the three stages of R-ISS. The C-statistic was significantly greater for R-ISS than for ISS (0.769 vs. 0.696, P<0.001). The event NRI was -0.08 (95% confidence interval [CI], -0.18-0.01) and the non-event NRI was 0.05 (95% CI, -0.03-0.10), resulting in a total NRI of -0.03 (95% CI, -0.14-0.08, P=0.602). The R-ISS performs well and has significantly better discriminative power than the ISS in MM patients treated with novel agents as a primary therapy. However, it does not better reclassify patients from the ISS, suggesting that there is still room to improve the staging system. Moreover, new statistical measures for assessing and quantifying the risk prediction of new prognostic models are necessary in future studies.