PLK1 and breast cancer: For example, PLK1 is overexpressed in a variety of cancers, including prostate cancer [24], non-small cell lung cancer [25], head and neck cancer [26,27], esophageal and gastric cancer [28], melanoma [29], breast cancer [30], ovarian cancer [31], endometrial cancer [32], colorectal cancer [33], glioma [34], thyroid cancer [35], and hepatocellular cancer [36].