Emerging evidence highlights the critical role of magnesium ion (Mg2+) homeostasis in tumor immunity and metastasis, with clinical implications centered on biomarkers and therapeutic strategies: Magnesium Homeostasis Scores (MHS), derived from transporter genes (e.g.: CNNM2, ANK3), may stratify immunotherapy responders and predict metastasis risk in breast cancer and melanoma [40], while Phase I/II trials in immunotherapy-resistant tumors suggest Mg2+ supplementation could enhance CD8 + T cell infiltration. The gene discussed is CNNM2; the disease is melanoma.