The inhibition of TDO2 decreased tumour metastasis by promoting the T cell response in vivo.9 Moreover, metalloproteinases that were secreted by CAFs promoted the release of Ras‐related C3 botulinum toxin substrate (Rac1b)/cyclooxygenase 2 (COX‐2)‐mediated reactive oxygen species in cancer cells, which is essential for EMT, cell stemness and metastasis.89 Additionally, CAFs promote angiogenesis through a complex interaction with cancer cells and macrophages. The gene discussed is PTGS2; the disease is cancer.