This study aimed to investigate the anti‐PD‐1 inhibitor pembrolizumab as a potential agent for use in non‐muscle‐invasive bladder cancer (NMIBC) by conducting a Phase 1 safety run‐in study to assess the safety and tolerability of intravesical pembrolizumab after transurethral resection of the bladder tumour (TURBT). This evidence concerns the gene PDCD1 and urinary bladder neoplasm.