Objective measures of physical functional capacity warrant exploration to complement or replace the subjective physician estimated performance status.

Performance status, a measure of physical functioning, can be influenced by several undefined physician and patient-related factors, and is inherently subjective. Although disappointing results in phase 3 trials may reflect a lack of improved outcomes due to biological mechanisms, a confounding effect of imbalances of physical functioning cannot be excluded in the context of modest increments in antitumor activity. Therefore, performance status estimation may complicate drug development, and an objective measure of physical reserve is desirable and may complement or outperform performance status. We explore and discuss attractive candidates for objective measures of physical functioning.