Although progression of Common Terminology Criteria for Adverse Events (CTCAE) grade 1 hypomagnesemia to grade 2 hypomagnesemia could be suppressed in some patients receiving intravenous magnesium infusion, there is no study whether patients could continue to receive anti-EGFR antibody with the additional magnesium infusion. Here, EGFR is linked to familial primary hypomagnesemia.