A translational modeling study challenged a core assumption behind pembrolizumab dosing. The work, published in the British Journal of Cancer, reports that receptor occupancy of PD-1 fails to reliably predict immune activation under pembrolizumab dosing conditions. Pembrolizumab is widely administered based on the idea that saturating PD-1 on T cells unlocks anti-tumor responses. The analysis instead suggests that PD-1 occupancy alone may not capture the downstream immunobiology driving clinical effect. For dosing strategy and clinical pharmacology, the finding matters because it pushes investigators toward better biomarkers—such as pathway-level signatures or functional readouts—rather than occupancy surrogates. It also raises the bar for any future attempt to optimize schedule and dose using receptor binding metrics. (Story coverage source: translational modeling report.)