All five patients with type 1 diabetes had metastatic disease with primary malignancies that included melanoma (n = 2), squamous cell lung carcinoma (n = 2) and lung adenocarcinoma (n = 1) and received therapy with PD-1 inhibitors (nivolumab or pembrolizumab) prior to developing type 1 diabetes. This evidence concerns the gene PDCD1 and melanoma.