F2R and carcinoma: F2R expression is upregulated in smooth muscle actin-positive breast fibroblasts surrounding carcinoma cells [28] and in activated fibroblasts in arteries and veins [29] An increase in F2R has been reported in various GI tumors including cholangiocarcinoma, colon adenocarcinoma, esophageal carcinoma, rectum adenocarcinoma, and in stomach adenocarcinoma, where higher F2R expression was associated with infiltration of a number of immune cell populations including CD4+ lymphocytes, macrophages, and eosinophils.