Highlights d Antibody blockade of MerTK prevents apoptotic cell clearance by macrophages d MerTK blockade induces tumor-cGAS-and host-STINGdependent type I IFN response d Extracellular ATP facilitates transfer of tumor-derived cGAMP to TAMs via P2X7R d MerTK blockade increases tumor immunogenicity and enhances anti-PD-1/PD-L1 therapy

AIMS: Neoadjuvant chemotherapy followed by surgery is the standard of care for patients with gastro-oesophageal adenocarcinoma. Previously, we validated the utility of the tumour regression grade (TRG) as a histopathological marker of tumour downstaging in patients receiving platinum-based neoadjuvant chemotherapy. In this study we profiled key DNA repair and damage signalling factors and correlated them with clinicopathological outcomes, including TRG response. METHODS AND RESULTS: Formalin-fixed human gastro-oesophageal cancers were constructed into tissue microarrays (TMAs). The first set consisted of 142 gastric/gastro-oesophageal cancer cases not exposed to neoadjuvant chemotherapy and the second set consisted of 103 gastric/gastro-oesophageal cancer cases exposed to preoperative platinum-based chemotherapy. Expressions of ERCC1, XPF, FANCD2, APE1 and p53 were investigated using immunohistochemistry. In patients who received neoadjuvant chemotherapy, favourable TRG response (TRG 1, 2 or 3) was associated with improvement in disease-specific survival (P ¼ 0.038). ERCC1 nuclear expression correlated with lack of histopathological response (TRG 4 or 5) to neoadjuvant chemotherapy (P ¼ 0.006) and was associated with poor disease-specific (P ¼ 0.020) and overall survival (P ¼ 0.040). CONCLUSIONS: We provide evidence that tumour regression and ERCC1 nuclear protein expression evaluated by immunohistochemistry are promising predictive markers in gastro-oesophageal cancer patients receiving neoadjuvant platinumbased chemotherapy.

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