Recent reports have shown that the interaction between PRL and cyclin M (CNNM) family Mg2+ transporter proteins, which comprise CNNM1–CNNM4 in mammals, is required for PRL-induced cancer malignancy (Wang et al., 2003; Funato et al., 2014; Hardy et al., 2015; Gulerez et al., 2016; Kozlov et al., 2020). This evidence concerns the gene CNNM4 and cancer.