PPP1R21 and gastric cancer: Multitudinous previously conducted clinical and experimental studies have shown that the association of PPP1R21 (PPP1R21) with the development of various tumors, including such as colorectal carcinoma [61,62], oral cancer (in mice) [63], thyroid carcinoma [64], lung cancer [65,66], small intestine tumor [67], and stomach cancer [68].