Complete response to pembrolizumab in a patient with metastatic colon cancer with microsatellite instability and a history of Guillain-Barre syndrome.

Currently, clinical trials with programmed death-1 (PD-1) inhibitors exclude patients with preexisting autoimmune disorders such as Guillain-Barre syndrome (GBS). Therefore, the scientific literature has limited information about the efficacy and safety of PD-1 inhibitors in cancer patients with autoimmune disorders. Immune checkpoint inhibitors can exacerbate preexisting autoimmune disorders and can induce severe immune-related adverse events. Here, we report the case of a 73-year-old female patient with history of GBS and mismatch repair deficient metastatic colorectal cancer who achieved a durable complete response to pembrolizumab. The patient was maintained on intravenous immunoglobulin (IVIG) during her treatment without any neurological exacerbations. This case highlights the feasibility of PD-1 inhibitors in select patients with neurological autoimmune disorders and calls for more systematic evaluation of checkpoint inhibitors in patients with cancer and GBS, especially with the known link between this disorder and malignancy.