POLE2 and breast cancer: Previous studies showed that POLE2 is overexpressed in many cancers, such as lung adenocarcinoma, breast cancer, colorectal cancer and esophageal squamous cell carcinoma (ESCC), and it can promote tumor development (Spier et al., 2015; Li et al., 2018; Pearlman et al., 2019; Zhu et al., 2020).