Rechallenge of programmed cell death 1 inhibitor after an interval with dacarbazine treatment may be effective for advanced malignant melanoma.

Immune checkpoint inhibitors (ICI) have been administrated as a standard medication in many cases of malignant melanoma (MM). They may be effective even for MM in advanced stages. However, it is still challenging to reduce the burden of MM, which were or became refractory to ICI, especially those without BRAF gene mutation. Re-administration of ICI after other modalities of treatment may be an option of treatment, but the efficacy and safety of retreatment with ICI have not been well established. We experienced four patients with advanced MM retreated with programmed cell death 1 (PD-1) inhibitor. All cases were refractory to the first PD-1 inhibitor, nivolumab, and then treated with dacarbazine (DTIC), followed by pembrolizumab. Two of the four cases achieved a partial response by switching to pembrolizumab as the second PD-1 inhibitor, and the other two cases resulted in progressive disease. In all cases, no new severe adverse events developed upon PD-1 inhibitor retreatment. Even if the first PD-1 inhibitor proves to be ineffective, it is worth re-administrating PD-1 inhibitor following a bridging therapy with DTIC.