Anti-programmed death receptor 1 (PD-1) drugs nivolumab and pembrolizumab were recently approved for the treatment of advanced melanoma and other solid tumors. Atypical patterns of response (i.e. tumor shrinkage or stabilization after initial progression) were observed in about 10% of metastatic melanoma patients treated with anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) drug ipilimumab and were associated with improved survival; however, the rate of atypical response patterns to anti-PD-1 therapy is not clear. An electronic search was performed to identify clinical trials evaluating response to anti-PD-1 therapy with nivolumab and pembrolizumab in patients with advanced solid tumors. Thirty-eight studies were included in our analysis for a total of 7069 patients with advanced cancer treated with anti-PD-1 therapy. Responses were evaluated by unconventional response criteria in 19 trials and were observed for all cancer types but tumors with mismatch-repair deficiency and head and neck squamous cell carcinoma. Overall, 151 atypical responses were observed in 2400 patients (6%) evaluated by unconventional response criteria. The results of our systematic review highlight the clinical relevance of unconventional responses to anti-PD-1 therapy and support further investigation into the development of tools that may assist evaluation of the antitumor activity of immunotherapy.
Keywords: Anti-PD-1; Lung cancer; Melanoma; Nivolumab; PD-1; Pembrolizumab.
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