PTGS2 and neoplasm: Second, stromal cells, such as endothelial cells and nerve cells, can release tumor progression-related soluble factors, including cyclooxygenase-2 (COX-2) [44, 45], prostaglandin E2 (PGE2) [45, 46], transforming growth factor-β (TGF-β) [47, 48] and vascular endothelial growth factor (VEGF) [49], which can regulate the T-cell response at multiple stages of cancer-immunity cycle.