In a separate phase I clinical trial (NCT03353402), investigators administered treatment to 10 patients with anti-PD-1-refractory metastatic melanoma who had previously attained complete response (CR) following nivolumab monotherapy, and assessed the safety and feasibility of nivolumab re-induction.29 Three subjects attained six-month progression-free survival, with two exhibiting partial response (PR) and one achieving CR. Here, PDCD1 is linked to metastatic melanoma.