Although Chk1 inhibitors—for example, AZD7762 [9,10], LY2603618 [11,12], and GDC-0575 [13]—also failed to induce anti-cancer effects as significant as those exerted by single agents, they have the potential, as chemosensitizers, to sensitize cancer cells to a variety of DNA-damaging agents. This evidence concerns the gene CHEK1 and cancer.