Tremelimumab-associated tumor regression following after initial progression: two case reports.

The human IgG2 monoclonal antibody tremelimumab is an immune checkpoint inhibitor that blocks cytotoxic T lymphocyte-associated antigen-4 (CTLA-4). The therapeutic response of anti-CTLA-4 monoclonal antibodies possess unique kinetics, in that antitumor responses are often observed after initial short-term disease progression, in some cases as long as 6-12 months after anti-CTLA-4 treatment initiation. Here, we report two cases: one of bile duct cancer and the other of squamous cell carcinoma of unknown primary, both of which demonstrated initial rapid disease progression followed by dramatic tumor shrinkage after one or two doses of tremelimumab, without any immune-related adverse events. This delayed, yet dramatic antitumor response suggests that tremelimumab may hold promise in the treatment of solid tumors.