The Revised International Staging System (R-ISS) was introduced as a powerful prognostic system to stratify patients with newly diagnosed multiple myeloma (NDMM). The serum-free light chain (sFLC) has been developed as a valuable marker to monitor multiple myeloma (MM) progression and response. Therefore, it is imperative to combine R-ISS and sFLC prognostic factors as modified R-ISS (MR-ISS) to better stratify patients into homogeneous survival subgroups, especially to further distinguish the high-risk MM patients who are likely to experience rapid progression or relapse. A total of 595 patients with NDMM were studied retrospectively. We performed the K-adaptive partitioning in 595 NDMM patients to define the MR-ISS classification: stage I includes R-ISS stage I and sFLC ratio < 80 (n = 66); stage III includes R-ISS stage III with sFLC ratio ≥ 80 (n = 87); stage II includes all the remaining conditions (n = 442). The median OS was not reached for MR-ISS stage I, 48.67 months for stage II, and 21.13 months for stage III. A significant OS difference of MR-ISS stage I and III patients has a particularly superior and inferior outcome compared with R-ISS stage I and III, respectively, which showed the similar results in PFS analysis. Validation of results was performed in an independent cohort. Our data indicate that the MR-ISS provides an improved prognostic power compared with R-ISS.
Keywords: Clinical outcome; Multiple myeloma; Revised International Staging System; Serum-free light chains.