A translational modeling study challenges a core assumption behind PD-1 immunotherapy dosing: that receptor occupancy can predict immune activation. The analysis, published in the British Journal of Cancer, reported that receptor saturation does not consistently map onto downstream immune activation in a pembrolizumab dosing framework. The finding directly affects how teams think about response biomarkers and how they interpret pharmacology endpoints in early development—especially for studies that rely on occupancy as a surrogate. For development organizations, the practical implication is that clinical pharmacology readouts may need to shift toward mechanistic markers closer to immune effector engagement rather than relying on PD-1 saturation alone.