CAST and cancer: The calpain family also consists of an endogenous inhibitor, calpastatin [4,13,14], which, under different physiological conditions, tightly regulates calpain–substrate interactions (Yadavalli et al., 2004) [15]; however, dysregulation of the activities of different calpains is observed in various cancers, probably through the downregulation of calpastatin (Zhang et al., 2019) [16].