Combined immunotherapy is associated with a significant risk of severe and potentially fatal immune-related adverse events (irAEs). Therefore, we retrospectively analyzed the side profile and efficacy of low-dose ipilimumab (1 mg/kg, IPI1) combined with anti-PD-1 immunotherapy in patients who progressed after anti-PD-1 monotherapy. Nine patients with unresectable stage III or IV melanoma treated with combined low-dose ipilimumab (1 mg/kg, IPI1) and anti-PD-1 immunotherapy, following progression after anti-PD-1 treatment, were identified. Treatment response and irAEs were recorded. Grade 3 irAEs occurred in one-third of patients. Interestingly, there were no grade 4 or 5 irAEs. In fact, four out of the nine patients experienced no irAEs at all. One patient discontinued combined immunotherapy due to immune-related colitis. The mean time to the onset of grade 3 irAEs was 14.3 weeks. The objective response rate was 33.3% and a disease control rate of 66.7% was achieved. Median progression-free survival (PFS) was 5.7 months and median overall survival (OS) was 21.6 months. The median PFS when IPI1 and anti-PD-1 treatment was administered in the second-line setting was not reached, but only 2.8 months when used in subsequent treatment settings. Combined IPI1 and anti-PD-1 immunotherapy was well tolerated. Its use in the third-line or above setting was associated with a significantly poorer prognosis than in the second-line setting. Larger, prospective studies are required to evaluate the safety and efficacy of this dosing regimen following anti-PD-1 treatment failure.
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