R-ISS (Revised ISS for Myeloma)

The Revised International Staging System (R-ISS) for multiple myeloma is an enhanced version of the ISS that incorporates cytogenetic risk and serum LDH alongside the original ISS staging. Published by Palumbo and colleagues in 2015 in the Journal of Clinical Oncology on behalf of the International Myeloma Working Group (IMWG), the R-ISS provides significantly improved prognostic discrimination.

The R-ISS was developed to address the well-recognized limitation that the original ISS does not account for biologic disease characteristics. Myeloma is genetically heterogeneous, and specific cytogenetic abnormalities have dramatic impact on outcomes. High-risk cytogenetics — particularly del(17p), t(4;14), and t(14;16) detected by fluorescence in situ hybridization (FISH) — are present in approximately 25% of patients and are associated with significantly shorter progression-free and overall survival.

The R-ISS defines three stages: R-ISS I (ISS Stage I + standard-risk cytogenetics + normal LDH) with approximately 82% 5-year OS, R-ISS III (ISS Stage III + either high-risk cytogenetics or elevated LDH) with approximately 40% 5-year OS, and R-ISS II (all others) with approximately 62% 5-year OS. This three-tier system provides excellent separation, particularly in identifying the worst-prognosis R-ISS III group.

Serum LDH was included because it reflects tumor cell proliferation rate and is an independent adverse prognostic factor in myeloma. Elevated LDH is associated with aggressive disease biology, extramedullary disease, and resistance to standard therapy. Its inclusion adds prognostic information beyond what ISS and cytogenetics alone provide.

The R-ISS has become the standard staging system recommended by IMWG and is required for risk stratification in most myeloma clinical trials. It is incorporated into NCCN, ESMO, and BSH guidelines. The system informs treatment intensity decisions, with R-ISS III patients often receiving more aggressive approaches including tandem transplantation, quadruplet induction regimens, and maintenance with novel agents.

Ongoing research is evaluating whether additional molecular features (gene expression profiling, minimal residual disease status, additional FISH abnormalities) can further refine the R-ISS. The recent development of the R2-ISS and the integration of 1q21 gain/amplification represent the next evolution of myeloma staging.