In recent years, the approval of anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and anti-programmed cell death protein 1 (PD-1) antibodies have led to significant improvements in disease outcomes for various cancers. Despite their long-term durable efficacy, the responses to immune checkpoint blockade are limited to a minority of patients. In an attempt to overcome this, the combination of CTLA-4 and PD-1 inhibitors is gaining momentum as a rational approach to improve outcomes.1 This review describes the mechanism of action of both nivolumab and ipilimumab and discusses how the combined use of both drugs leads to potential synergism. The final part of the article assesses the extent to which this theoretical synergism is translated into a clinical benefit for cancer patients.