A new staging system for multiple myeloma patients based on the Southwest Oncology Group (SWOG) experience

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Abstract
Summary.We aimed to develop and evaluate a staging system for multiple myeloma (MM) based on easily obtained laboratory measures. The Durie–Salmon stage is most commonly used and is an effective system of patient stratification for clinical trial research. However, the criteria are complex and many laboratory parameters are required to properly stage patients. In this analysis, we focused on two common measures with prognostic importance in MM: serum β2 microglobulin (β2m) and serum albumin. Pre‐study data on 1555 previously untreated MM patients enrolled on four recent South‐west Oncology Group (SWOG) phase III trials were used in the analysis. Staging models were developed and validated using regression tree methods for survival outcomes. SWOG stages were defined as: stage 1, β2m < 2·5 mg/l (14% of patients, median overall survival of 55 months); stage 2, 2·5 ≤ β2m < 5·5 (43% of patients, median overall survival of 40 months); stage 3, β2m ≥ 5·5 and albumin ≥ 30 g/l (32% of patients, median overall survival of 24 months); and stage 4, β2m ≥ 5·5 and albumin < 30 g/l (11% of patients and median overall survival of 16 months). This staging scheme was also predictive of event‐free survival, first‐year mortality and long‐term (≥ 5 years) event‐free survival. We conclude that although the SWOG stage does not represent a new prognostic marker for MM (cytogenetics, FISH), it could provide a simple alternative to the Durie–Salmon stage for patients with previously untreated MM. Additional evaluation in other MM patient populations is needed to confirm results.