MMP9 and neoplasm: In Gastric cancer, single-cell RNA sequencing post-PD-1 therapy identified increased circulating neutrophils, with the NE-1 subset exhibiting an activated phenotype (high MMP9, S100A8, S100A9, PORK2, TGF-β1 expression) and interacting with malignant epithelial cells and M2 macrophages via chemokine pathways to promote tumor progression [180].