An important target of miR-221/222 is the CDK inhibitors p27Kip1, one of the most important cell cycle regulator, which has relevant impact on the proliferation and cell cycle control in a variety of human malignancies, including prostate carcinoma [40], glioblastomas [35], thyroid carcinomas [44], breast cancer [45], hepatocellular carcinoma [46], and lung cancer [47]. Here, CDKN1B is linked to breast cancer.