The Value of Risk Stratification Tools in Multiple Myeloma (MM) in the Real-World: Validation of the Revised- International Staging System (R-ISS) at Initiation of Treatment and Relevance of the ISS and the R-ISS for Risk Stratification in the Relapsed Setting Using Data from the Czech Registry of Monoclonal Gammopathies (RMG)

The ISS stratifies survival risk in patients with MM based on β₂-microglobulin and albumin levels. The R-ISS is an improved stratification tool, which also uses chromosomal abnormalities (CA) and lactate dehydrogenase (LDH). It was developed based on clinical trial data in the first-line setting but, has not been validated outside clinical trials or for use in the relapsed setting. Using data from the RMG, we assessed the real-world validity of the R-ISS at diagnosis. Additionally, as it is standard practice to re-stage patients after first relapse, we explored the value of re-estimating ISS stage in the relapsed setting and exploring the carry on effect of R-ISS from diagnosis. Re-estimation of R-ISS at relapse is not possible as standard practice often does not include CA measurement at first relapse. Assessment of improvement in stratification was based on visual comparison of median OS, hazard ratios (HR) and confidence intervals.

Eligible patients were diagnosed with symptomatic MM between May 2007 and April 2016. A Cox regression model and Kaplan-Meier analyses assessed the performance of the ISS and R-ISS for stratifying patients based on survival both at diagnosis and at first relapse.

Overall, there were 3027 patients at diagnosis however only 493 were included in these analyses due to unavailable CA values (84% of patients). ISS and R-ISS stage distribution at diagnosis was ISS I 31.2%, II 29.1% and III 39.6%; and R-ISS I 12% II 57% and III 31% (Table 1). Median overall survival (OS) in months (95% confidence interval [CI]), from diagnosis was 73.5 (68.0-NE), 40.5 (31.0-50.0) and 29.0 (20.9-37.2) in patients with ISS stage I, II and III, respectively, and not reached (NR), 46.6 (39.2-54.1) and 26.0 (18.2-33.8) in patients with R-ISS stage I, II and III, respectively. Table 2 shows HR, which indicate OS assessed in alternative ways was significantly different among the three stages for both ISS and R-ISS. R-ISS provided refined stratification than ISS alone, since R-ISS stage III classified patients with higher risk than ISS III alone, (shorter median OS, narrower CI, and stronger HR vs. ISS I and II). From the original sample of 493 patients at diagnosis, only 250 went on to receive further treatment after first relapse. The median OS months (95% CI) after first relapse was 46.4 (32.0-60.8), 22.8 (13.4-32.1) and 14.9 months (9.0-20.8) in patients staged as ISS stage I, II and III at diagnosis, respectively. In patients staged as R-ISS stage I, II and III at diagnosis it was NR, 25.6 (20.8-30.3) and 10.4 (6.7-14.2), respectively. Data to enable re-estimation of ISS and R-ISS at first relapse were available for 187 patients (R-ISS re-stratification was using CA data at diagnosis only). Median OS months (95% CI) from first relapse was 32.2 (15.5-49.0), 25.6 (11.5-39.6) and 10.8 (8.6-13.0) in patients at ISS stage I, II and III, respectively, and 23.3 (NE-NE), 28.4 (20.8-36.0) and 9.7 (6.5-12.9) in patients at R-ISS stage I, II and III, respectively. The HRs comparing OS from first relapse stratified by ISS at diagnosis indicated that re-estimating ISS did not improve stratification (Table 2). For R-ISS, compared with staging patients at diagnosis, staging at first relapse resulted in refined stratification between stage II and III, however assessment of HRs comparing to stage I was difficult owing to small sample sizes. Re-estimation of R-ISS stage at first relapse resulted in 26% of patients having their stage reclassified; the main drivers of reclassification to a lower R-ISS risk group were β2-microglobulin and albumin levels, and to a higher risk group, LDH levels.

Our real-world data show that, at diagnosis R-ISS provides refined risk stratification compared with ISS. Further refinement seemed to be added by restaging at first relapse using R-ISS, not ISS however, CA measurements are not currently routinely measured at first relapse, limiting the practical utility of the R-ISS at this stage. Therefore, re-estimating R-ISS stage after first relapse may enable physicians improve estimation of patient prognosis. Both ISS and R-ISS have been developed for use at diagnosis when there is less evidence to predict prognosis, therefore risk stratification after first relapse should also consider other historical patient, disease and treatment factors contributing to improved risk stratification and improved treatment selection and outcomes.

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