The successful treatment of a patient with metastatic small-cell bladder carcinoma with pembrolizumab [5], a programmed cell death protein 1 (PD-1) inhibitor, has led to an ongoing phase II study (NCT03430895) to evaluate anti-checkpoint therapies in patients with rare bladder cancer entities including small-cell carcinoma. Here, PDCD1 is linked to urinary bladder carcinoma.