Evaluation of the Revised International Staging System (R-ISS) in Japanese patients with multiple myeloma

In spite of recent development in the treatment armamentarium for multiple myeloma, overall survival (OS) still depends on risk status and sensitivity to treatment of each patient. We have evaluated the clinical relevance of the Revised International Staging System (R-ISS) by comparing it with the original ISS in 718 Japanese patients. The distribution of patients according to response was similar between the ISS and R-ISS stages. Treatment response was greatly influenced by initial treatment modalities and deeper response was observed more frequently in transplanted patients. The R-ISS discriminated the difference in OS between the stages more distinctly than the ISS (p = 9.0 × 10^-15 and p = 4.0 × 10^-10, respectively). Differences in OS were clarified by both R-ISS and ISS in non-transplanted patients (p = 2.4 × 10^-12 and p = 1.4 × 10^-8, respectively), but the ISS failed to distinguish the difference between the stages in transplanted patients (p = 0.13). In contrast, the R-ISS could at least discriminate the excellent prognosis of stage I patients whereas the distinction between stage II and III was not that clear (p = 0.033). The R-ISS stage II encompassed a large number of patients, and the prognosis was heterogeneous depending on the fulfillment of prognostic factors such as LDH and adverse cytogenetics. These results suggest that treatment factors and prognostic factors greatly affect the therapeutic response and outcome, and the R-ISS is superior to ISS in prognostication of both transplant-eligible and -ineligible patients in our current clinical practice.