TK1 and cancer: Numerous studies have further demonstrated that elevated TK1 levels have occur in the serum of many different types of cancers, including some of the most common cancers of the lung cancer, colon cancer, and breast cancer (Alegre et al., 2012; Jagarlamudi & Shaw, 2018; Topolcan & Holubec, 2008; Zhou et al., 2013).