"Antitumor activity"@en . "Pembrolizumab"@en . "Janice M. Mehnert" . . "Pancreatic neuroendocrine tumors"@en . . "35d8927e0c843f8a815bf11baed20ca5" . "Janice M." . "Carcinoid tumors"@en . "Immunotherapy"@en . "KEYNOTE-028"@en . "Mehnert" . "Programmed death\u2013ligand 1"@en .