CTLA4 and acute kidney injury: AKI occurred at a median time of 14 weeks, grade 3 in about 57% and requiring renal replacement therapy in 9% with persistent renal damage in 15%. At rechallenge with CPI, recurrence rate was of 23%. Risk factors include use of PPI, lower eGFR at baseline and concomitant anti-PD1 and anti-CTLA4 therapy. Renal biopsy should be always performed.