The Sokal Score is a medical tool used to understand the likely course of chronic myeloid leukemia (CML), a type of white blood cell cancer. Applied at the time of diagnosis, this scoring system classifies patients into different risk categories. This helps predict long-term outcomes for those living with CML.
What is the Sokal Score?
The Sokal Score, also known as the Sokal Index, originated from research by Joseph E. Sokal and colleagues between 1962 and 1981. It was developed to assess the prognosis of CML patients in its chronic phase. The score’s primary purpose is to stratify patients into low, intermediate, or high-risk groups, indicating their long-term survival prospects. This stratification was initially based on outcomes for patients treated with older chemotherapy agents like busulfan or interferon, predating modern targeted therapies.
How the Sokal Score is Calculated
The Sokal Score is determined using a specific mathematical formula incorporating several patient characteristics and laboratory findings. Variables include age in years, spleen size (centimeters below the costal margin), platelet count, and the percentage of myeloblasts (immature white blood cells) in peripheral blood. These values are entered into the formula: Sokal Score = exp([0.0116 × (age in years – 43.4)]) + [0.0345 × (spleen size in cm – 7.51)] + [0.188 x ((platelets in 10^9/L / 700)^2 – 0.563)] + [0.0887 × (blasts in % – 2.10)], where ‘exp’ denotes the exponential function.
After calculation, patients are assigned to one of three risk categories based on specific score ranges. A score less than 0.8 places a patient in the low-risk group. Scores between 0.8 and 1.2 correspond to an intermediate-risk classification. A score greater than 1.2 indicates a high-risk group.
Clinical Significance and Application
The Sokal Score helps clinicians make informed decisions regarding treatment strategies. Patients categorized into low, intermediate, or high-risk groups have historically shown different survival rates. For instance, studies estimated five-year progression-free survival for low-risk scores at 92%, intermediate risk at 93%, and high-risk at 73%.
Patients identified as low or intermediate risk might initially be considered for standard-dose imatinib, a common targeted therapy. Those in the high-risk category may be evaluated for newer generation tyrosine kinase inhibitors (TKIs) or require closer monitoring to ensure a complete molecular response. The Sokal Score is also used in clinical trials to ensure consistency and allow comparisons with historical data.
Considerations and Evolving Practices
While the Sokal Score holds historical importance in CML prognostication, it was developed before the widespread use of modern tyrosine kinase inhibitors (TKIs). Its predictive accuracy for current treatment outcomes, which have significantly improved with TKIs, can be limited. Survival rates are much higher today than when the score was first devised.
Newer prognostic scoring systems, such as the European Treatment and Outcome Study (EUTOS) score and the EUTOS Long-Term Survival (ELTS) score, better reflect outcomes in the TKI era. These models offer improved accuracy in identifying high-risk patients and predicting long-term survival with contemporary therapies. Although the Sokal Score is still referenced in some clinical guidelines and for historical comparisons, it is frequently used alongside or being superseded by these more recently developed and validated prognostic tools.