CCND1 and cancer: Since CCND1 is a key gene controlling cell cycle and it is frequently overexpressed in cancer cells, contributing to cell proliferation and migration [20], we thought that CCND1 would be an idea gene for microRNA target validation because a few microRNAs have been previously validated, such as miR-17/20 [21], miR-16 family [22,23], and let-7 [24]; and a relatively large number of microRNAs are predicted to target CCND1.