ICOS and gastric cancer: Recently, with a growing numbers of studies focusing on the immunophenotype of TILs, an increased percentage of ICOS+ Tregs have been observed in more and more types of tumor tissues, including melanoma, (134) head and neck squamous cell cancers, (135) gastric cancers, (136) breast cancer, (137) ovarian cancer, (138) clear cell renal cell carcinoma, (139) and acute myeloid leukemia (AML) (140).