The clinical impact of precise assessment of predictive biomarkers in gastroesophageal cancer: focus on the PD-L1 combined positive score (CPS) and tumor area positivity (TAP) systems

Accurate assessment of PD-L1 expression is crucial for therapeutic decision-making in esophageal, esophago-gastric junction, and gastric cancers, where immune checkpoint inhibitors have become integral to first-line treatment in selected patients. This review provides an updated, practice-oriented summary on PD-L1 immunohistochemistry evaluation, with emphasis on the emerging Tumor Area Positivity (TAP) scoring system together with established Combined Positive Score (CPS) and Tumor Proportion Score. First, we examine the clinical relevance and use in clinical trials of each scoring method, and the pre-analytical and analytical variables influencing PD-L1 interpretation. Then, we address advantages and disadvantages of each scoring system, including a thorough analysis and pictorial interpretation guide of the recently introduced TAP score. Indeed, thanks to a visual-estimation-based assessment of PD-L1 expression, TAP has improved reproducibility and reduced scoring time, but large-scale validation is ongoing and certain interpretive challenges remain. Finally, we propose a standardized reporting template to enhance consistency in diagnostic practice, together with our perspective on future improvements and challenges of PD-L1 assessment.