What does ECOG (Eastern Cooperative Oncology Group) measure?

What ECOG Measures

The Eastern Cooperative Oncology Group (ECOG) Performance Status scale measures a patient's functional status and level of physical activity, specifically assessing their ability to perform daily activities, work capacity, and degree of ambulatory independence. 1

Core Assessment Domains

The ECOG scale quantifies functional status based on:

• Ambulatory status and mobility - the patient's ability to walk and move independently 1
• Self-care abilities - capacity to perform basic activities of daily living 1
• Symptoms and their functional impact - how disease manifestations limit activity 2
• Need for care and assistance - degree of dependence on others 2
• Time spent in bed during daytime - proportion of waking hours confined to bed 2

The ECOG Scale Structure

The scale uses a 5-point ordinal system (0-4) where: 2, 3

• ECOG 0 = Normal activity, fully active, no restrictions
• ECOG 1 = Some symptoms present but still near fully ambulatory, restricted in physically strenuous activity
• ECOG 2 = Ambulatory and capable of self-care but unable to work, up and about more than 50% of waking hours
• ECOG 3 = Capable of only limited self-care, confined to bed or chair more than 50% of waking hours
• ECOG 4 = Completely disabled, cannot carry out any self-care, totally confined to bed or chair

Clinical Significance and Prognostic Value

ECOG performance status is one of the most common eligibility criteria in oncology clinical trials and serves as a powerful prognostic indicator. 1

• Lower ECOG scores (0-1) correlate with better survival outcomes - patients with high-functioning status have significantly longer overall survival and progression-free survival compared to those with ECOG 2-4 1
• ECOG 2-4 predicts higher treatment toxicity risk - patients with poorer functional status are more likely to experience severe adverse events and may struggle to complete treatment courses 1
• Most clinical trials restrict enrollment to ECOG 0-1 - approximately 98% of patients in chemoradiotherapy trials had ECOG PS 0-1, with only 2% having ECOG PS 2 1

Important Limitations and Caveats

The ECOG scale is inherently subjective and susceptible to inter-observer variability and bias. 1

• Moderate inter-rater reliability - studies show only moderate non-chance agreement (Kappa 0.44) when all ECOG categories are considered, though agreement improves when distinguishing ECOG 0-2 versus 3-4 (92% and 82% probability of agreement, respectively) 2
• Age-related bias exists - clinicians tend to assign higher (worse) ECOG scores to patients over 65 years despite no objective difference in physical activity 1
• Less predictive in elderly populations - ECOG PS has reduced prognostic value for cancer-related outcomes in older adults 1
• Does not differentiate etiology - the scale cannot distinguish whether poor performance status results from cancer burden (potentially reversible with treatment) versus comorbidities or other factors 1

Comparison to Other Performance Scales

The ECOG scale differs from the Karnofsky Performance Status (KPS), which uses an 11-level scale (0-100) 4, 3. While both scales are widely used and strongly correlated (Spearman R = -0.869), ECOG PS demonstrates better predictive ability for discriminating patients with different prognoses compared to KPS 3. The Palliative Performance Scale (PPS) expands beyond both by incorporating additional domains including oral intake 4.