Creatinine Clearance Is More Important Prognostic Factor Than ß2 Microglobulin in Multiple Myeloma.

In the new staging system of multiple myeloma (MM) by South West Oncology Group (SWOG), the concentration of serum β2 microglobulin (β2m) and serum albumin were focused as the most important prognostic factors for survival.

However, serum concentration of β2m has been known as an indicator of glomerular filtration rate. The aim of this study was to compare the prognostic value of the level of β2m with that of creatinine clearance (Ccr) in patients with multiple myeloma. Retrospectively, from January 1, 1996 to November 30, 2003, we reviewed 176 MM patients (M: F 110:66 mean age: 58.5±11.0) whose 24-hour urinary creatinine clearance was available at the time of diagnosis. We collected clinical data such as hemoglobin, serum creatinine, calcium, albumin, β2m, creatinine clearance before chemotherapies, and patients’ survival time. Pretreatment β2m was inversely related to Ccr (Spearman’s correlation coefficient = −0.781, P <0.01). In univariate analysis, relative risk (RR) of death was 1.047 (p< 0.001) for β2m and 0.985 (p< 0.001) for Ccr. But multivariate analysis using Cox’s proportional hazard model showed β2m was not significant prognostic factor in patients’ survival after adjustment for Ccr (RR 1.025, p=0.054) but Ccr was an independent risk factor of death after adjustment for β2m (RR 0.990, p=0.013). And univariate analysis identified that RR for β2m is not significant in 88 MM patients (66 patients with β2m ≥ 2.5mg/l) with relatively normal renal function (Ccr ≥ 50 ml/min) (RR = 1.110, p=0.306)

We could propose another new staging system with β2m replaced by Ccr in SWOG staging system. The stages were defined as: stage 1, Ccr ≥ 80ml/min; stage 2, 50< Ccr <80; stage 3, Ccr < 50 and albumin ≥ 3.0g/dl; and stage 4 Ccr < 50 ml/min and albumin< 3.0 g/dl. According to this proposed staging system, median survival time of each stage from 1 to 4 is 1475, 887, 513, and 196 days, respectively. (Log Rank test < 0.0001)

In conclusion, Ccr could be more important prognostic factor than the level of β2m in patients of MM and we propose that Ccr should be reassessed as the component of staging system of MM.