Regarding crucial biomarkers for BC, studies detecting the association between PLK1 and ER status (seven studies with 1155 patients) [15–18, 21–23], PR status (five studies with 1745 BC patients) [13, 15, 17, 21–23], HER2 status (four studies 1240 BC patients) [13, 15, 17, 22], and p53 mutation status (three studies including 713 patients) [16, 17, 21] were included. The gene discussed is PLK1; the disease is breast cancer.