Abstract
Immunotherapy combinations are used to improve outcomes in metastatic cancer, but evidence-based knowledge of appropriate starting doses for novel combinations is lacking. Phase I-III adult combination clinical trials (≥ 1 drug was immunotherapy; anti-PD-1, PD-L1, or CTLA-4) were reviewed (PubMed Jan 1, 2010 to Sep 1, 2016; ASCO 2014-2016, ASH/ESMO 2014-2015 abstracts). The safe dose for each drug used in each combination was divided by the single-agent recommended dose to calculate dose percentage. Additive dose percentage was the sum of each dose percentage. Overall, 84 studies (N = 3,526 patients, 59 combinations) were analyzed. In 50% of studies, all drugs could be administered at full dose; 63%, in the presence of anti-PD-1/PD-L1 and 36% with anti-CTLA-4. The lowest safe starting dose for a doublet combination including a second immunotherapy was 50% of each drug; 60%, for a targeted agent. Most doublet/triplets combining anti-PD-1/PD-L1 with cytotoxics were tolerable at full doses. Response rates (median [interquartile range]) were higher for 3-drug than 2-drug combinations (53% [33-63%] (N = 23 studies) vs. 23% [14-39%]) (N = 60 studies) (p < 0.0001) with similar rates seen for targeted, cytotoxic, biologic, or additional immunotherapy combinations (p = 0.35). In conclusion, anti-PD-1/PD-L1 checkpoint inhibitors can be safely given with a variety of other immunotherapy and targeted agents, albeit at about half dose. Doublet and triplet combinations with cytotoxics could mostly be given at full doses. Anti-CTLA-4 agents compromised dosing more than anti-PD-1/PD-L1 agents. Response rates were significantly higher for 3- versus 2-drug combinations.