Pseudoprogression with subsequent complete response and severe thrombocytopenia to checkpoint inhibitor immunotherapy in a patient with advanced mucosal melanoma of the sinonasal cavity.

In this case report, we describe a patient with an inoperable mucosal melanoma of the sinonasal cavity who achieved an ongoing complete response to combined immunotherapy with ipilimumab and nivolumab after initial pseudoprogression. Despite massive enlargement of the tumor 9 weeks after treatment initiation, we decided to continue with checkpoint inhibitor immunotherapy because of lacking potent therapeutic alternatives and the possibility of pseudoprogression. In the computed tomography scan 3 months later, the tumor was no longer detectable.