A translational modeling study in the British Journal of Cancer challenged a core assumption behind pembrolizumab dosing—that receptor occupancy alone predicts immune activation. The work reported that saturating PD-1 on T cells did not consistently translate into downstream immune response signals, raising the likelihood that additional pharmacodynamic factors drive clinical effect. For drug development, the findings reinforce a shift from simplistic biomarker-to-response linkages toward more system-level immune measures. Clinicians and modelers are likely to revisit how PD-1 exposure is translated into activation kinetics when designing dosing strategies and trial endpoints.