Dynamic Changes in International Staging System As a Predictor of Survival Outcome in Patients with Advanced Multiple Myeloma

Background: The International Staging System (ISS) based on serum beta-2 microglobulin and serum albumin is a useful tool for risk stratification in patients with multiple myeloma. ISS is usually assessed at the time of diagnosis. Recent studies have suggested that risk stratification should be considered dynamic over the disease course. Our study aimed to describe dynamic changes in ISS over time and their impacts on mortality in patients with advanced multiple myeloma.

Methods: This study included 417 patients with multiple myeloma from the Flatiron medical records database (Jan 2011- May 2018) who have received at least two lines of therapy and had data on ISS at the time of diagnosis (T_DX) and at the time of initiating the second line of therapy (T_2L). ISS stage was either abstracted from medical records or derived from the results of laboratory tests of serum beta-2 microglobulin and serum albumin. Patients were followed up from T_2L until the earliest event of the last activity in database or death. We calculated mortality rates by T_DX and T_2L ISS stages, and generated Cox proportional hazard models to estimate the impact of T_DX and T_2L ISS stages on mortality. Additionally, in the subgroup of patients in ISS stage III at T_DX, we used univariate logistic models to identify the predictors for downward shift to ISS stage I or II at T_2L.

Results: The study cohort had a median age of 70 (interquartile range: 61 to 77), and 59% were male. Based on ISS at T_DX, 30%, 37%, and 33% of the study cohort were classified as stage I, II, and III with the mortality rate of 12, 11, and 24 deaths per 100 person-years, respectively. The hazard ratios were 0.95 (95% confidence interval (CI): 0.57-1.61) for patients in stage II and 1.96 (95% CI: 1.22-3.16) for patients in stage III, compared with patients in stage I. Based on ISS at T_2L, 47%, 34%, and 20% were classified as stage I, II, and III, with the mortality rate of 7, 19, and 39 deaths per 100 person-years, respectively. The hazard ratios were 2.62 (95% CI: 1.61-4.25) for patients in stage II and 5.18 (95% CI: 3.10-8.64) for patients in stage III, compared with patients in stage I.

Dynamic changes in ISS stages over time and mortality rates were depicted in the Table. Among patients in ISS stage I at T_DX, about 25% shifted to higher stages at T_2L, and had a higher mortality rate (26 per 100 person-years) than did patients remaining in stage I (8 per 100 person-years). For patients in ISS stage II at T_DX, 43% stayed in Stage II at T_2L, and 46% moved down to Stage I, with a mortality rate of 20 and 5 per 100 person-years, respectively. Among patients in ISS stage III at T_DX, 58% moved down to lower stages at T_2L. The mortality rate was 10, 21, and 40 per 100 person-years for patients moving down to Stage I and II at T_2L and those remaining in Stage III, respectively. In the subgroup of patients in ISS stage III at T_DX, strong predictors for shifting down to lower stages were younger age (odds ratio: 2.65; 95% CI:1.20-5.87 for age <65 vs ≥65 years) and serum creatinine ≤ 2 mg/dL at T_DX (odds ratio: 2.26; 95% CI:1.03-4.92 for serum creatinine ≤ 2 vs >2 mg/dL), but not gender, race, or cytogenetic abnormality of del17p, t(4;14), and t(14;16).

Conclusion: Large changes in ISS stages were observed in multiple myeloma patients when advancing the line of therapy. Changes in ISS stage were also associated with survival outcome. A downward shift to stage I was associated with substantially improved overall survival; in contrast, patients moving up to or remaining in higher stages had poor outcomes, especially for those remaining in ISS stage III. Our results suggest that re-evaluating ISS stage at the time of change in line of therapy can improve prediction of survival outcomes.

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