WPSS (WHO Prognostic Scoring System)

The WPSS (WHO Classification-Based Prognostic Scoring System) is a dynamic prognostic model for myelodysplastic syndromes that integrates WHO morphologic classification, cytogenetic risk groups, and transfusion dependency. Developed by Malcovati and colleagues in 2007 and published in the Journal of Clinical Oncology, the WPSS is unique among MDS prognostic systems because it can be applied at any time during the disease course, not just at diagnosis.

The WPSS was developed to address a key limitation of the original IPSS: the IPSS was validated only at the time of initial diagnosis, yet MDS is a dynamic disease that evolves over time. Patients may experience worsening cytopenias, increasing blast percentages, new cytogenetic abnormalities, or transformation to a higher-risk WHO category. The WPSS can capture these changes and provide updated prognostic information at any point during follow-up.

The system evaluates three variables: WHO morphologic category (reflecting blast percentage and lineage dysplasia), cytogenetic risk group (good, intermediate, or poor), and transfusion dependency (present or absent). The inclusion of transfusion dependency is distinctive, as it reflects the clinical impact of bone marrow failure and has been shown to be an independent adverse prognostic factor even after adjusting for hemoglobin level.

WPSS defines five risk groups: very low (0-1 points, median survival ~12 years), low (2 points, ~4.8 years), intermediate (3 points, ~2.2 years), high (4 points, ~1.2 years), and very high (5-6 points, ~0.8 years). These groups show excellent separation of survival curves and correlate with risk of AML transformation.

The WPSS's ability to be recalculated over time makes it particularly useful for monitoring disease progression and for timing treatment decisions. For example, a patient who transitions from low-risk to intermediate-risk WPSS may need to be reconsidered for more aggressive therapy or transplant evaluation. Serial WPSS assessment provides a framework for dynamic treatment planning.

Transfusion dependency in the WPSS is defined as having at least one red blood cell transfusion every 8 weeks over a 4-month period. This threshold was determined to have the best prognostic discrimination. Regular transfusion requirements not only reflect disease severity but also expose patients to complications including iron overload, alloimmunization, and transfusion reactions.