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PD-L1 expression testing (22C3, SP142, SP263)

aka PD-L1 expression, PD-L1-positive, PD-L1 positive, PD-L1-negative, PD-L1 negative, PD-L1-high, PD-L1 high, PD-L1-low, PD-L1 status, PD-L1 IHC, 22C3, SP142, SP263, 28-8, PD-L1 ≥50%, PD-L1 ≥1%

A stain on the tumour biopsy that measures how much of the PD-L1 'don't attack me' protein is present. Higher levels usually mean checkpoint inhibitors work better, and many approvals require a minimum score.

Several antibody clones (22C3 for pembrolizumab, SP142 for atezolizumab, SP263 for durvalumab, 28-8 for nivolumab) and scoring systems (tumour proportion score, combined positive score, immune cell score) are in use and are only partly interchangeable (Blueprint project), which complicates practice. PD-L1 ≥50% TPS in lung cancer permits pembrolizumab alone; CPS ≥10 gates pembrolizumab in triple-negative breast and CPS ≥1 or ≥5 in gastric and head and neck cancer. It is an imperfect biomarker: PD-L1-negative tumours sometimes respond and expression is heterogeneous and changes with treatment.

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PD-L1 expression testing (22C3, SP142, SP263)

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