Among the 36 studies, 25 studies [3, 6, 9, 11–17, 19, 22, 28, 30, 33, 36–41, 43, 46, 47, 50] assessed the association between low circadian clock genes expression and clinicopathological features in patients with cancers, and 22 studies [3, 6, 12–15, 19, 22, 24, 27, 28, 29, 30, 32, 33, 34, 41, 42, 47–50] investigated the relationship between low expression of circadian clock genes and OS in multiple cancers. Here, CLOCK is linked to cancer.