In contrast, calpain-2 played an important role in the nucleocytoplasmic trafficking of forkhead box protein P1 (FOXP1) via the PI3K-AKT pathway in breast cancer patients; cytoplasmic relocalization of FOXP1 correlated with reduced overall survival in breast invasive ductal carcinoma patients (Yu et al., 2018). Here, FOXP1 is linked to breast cancer.