Prognostic value of pretreatment serum β₂ microglobulin in myeloma: A Southwest Oncology Group Study

Six hundred twelve eligible, previously untreated patients with active multiple myeloma and at least some data available for analysis were entered into a randomized trial (Southwest Oncology Group [SWOG] Phase III myeloma study 8229/30), in which the prognostic significance of pretreatment serum β₂ microglobulin levels was evaluated. Because there was no statistically significant survival difference between the alternating and syncopating VMCP/VBAP regimens, it was possible to evaluate serum β₂ microglobulin for the total population all together. The serum β₂ microglobulin measurements showed the highest significance of any prognostic factor, both in the bivariate and multivariate regression analyses. The median survival was 36 months for the 322 patients with pretreatment serum β₂ microglobulin values of < 6 μg/mL, as compared with a median survival of 23 months for the 225 patients with a β₂ level of ≥ 6 mcg/mL (P < .0001). The stepwise multiple regression model first contained serum β₂ microglobulin, followed by serum albumin, serum calcium, age, and serum creatinine. Serum β₂ microglobulin was highly correlated with stage: median values ranged from 3.7 μg/mL for stage IA, to 10.1 for stage IIIB. It was possible to stratify myeloma patients based on combinations of serum β₂ microglobulin with both albumin and age, producing excellent separation of patients into low-, intermediate-, and high-risk categories. It is concluded that serum β₂ microglobulin is the most powerful prognostic factor currently available for multiple myeloma and that it can be used alone or in combination with other variables for pretreatment stratification.