Pembrolizumab treatment of metastatic urothelial cancer without exacerbating myasthenia gravis

Pembrolizumab is an immune checkpoint inhibitor (ICI) that targets the programmed cell death (PD)-1 receptor. It significantly increases the overall survival in patients with locally advanced or metastatic urothelial cancer. However, its administration may induce serious immune-related adverse effects, such as myocarditis and myasthenia gravis (MG). Therefore, ICI treatment may have been withheld for MG patients with cancer. We report the first case in which pembrolizumab was used safely without aggravation of MG symptoms in right renal pelvic and bladder cancers, even though the anti-acetylcholine receptor antibody (anti-ACh-R Ab) serum concentration increased. The patient was a 70-year-old man diagnosed with stage III renal pelvic cancer and bladder cancer, with multiple liver metastases. He was previously diagnosed with MG at the age of 58 years. During second-line treatment with pembrolizumab, his anti-AChR Ab levels increased from 0.8 to 10.9, without exacerbation of MG symptoms. The liver metastases disappeared after five courses of pembrolizumab. This report shows that MG is not a reason to refrain from using PD-1 inhibitors in cancer patients; it should be considered when treatment is performed in highly experienced centers.