PLK1 and Familial prostate cancer: PLK1 is frequently overexpressed in a variety of malignancies, including prostate cancer, breast cancer, and colorectal cancer (Strebhardt & Ullrich, 2006; Takai et al, 2005; Weichert et al, 2004), where its high expression correlates with poor prognosis and enhanced tumor growth (Maire et al, 2013).