PLK1 and breast cancer: Specifically, eight studies [13, 15, 16, 18, 21–23] including 1779 patients reported on the relationship between PLK1 and patient age; seven [13, 15–17, 21–23] provided sufficient pathological grading information for 1989 BC patients; seven [13, 15–18, 21–23] provided sufficient lymph node information for 2110 BC patients, and three studies with 1129 patients provided [13, 15, 22] sufficient tumor type information.