PLK1 and breast cancer: Considering the crucial role of PLK1 during DNA damage repair and cell-cycle regulation, it is not astonishing that it is upregulated in various types of cancers, such as melanoma, colorectal cancer, non-small cell lung cancer, thyroid carcinoma, esophageal carcinoma, ovarian carcinoma, colorectal cancer, breast cancer, and prostate cancer [3,4,5].