F2RL1 and gastric cancer: Mast cells secrete tryptase through the activation of protease-activated receptor-2 (PAR2), mitogen-activated protein kinase (MAPK), and the c-kit receptor;The density of tryptase-positive mast cells has a substantial correlation with the density of lymph node metastases in primary gastric cancer tissue and the prognosis of gastric cancer patients [51, 52].