Immune-checkpoint inhibitors (ICIs) have widened the therapeutic scenario of different cancer types. Phase I/II trials have been designed to evaluate the role of ICIs both as single agents and in combination in neuroendocrine neoplasms (NENs), but as yet no randomized controlled phase III trials have been carried out. A systematic review and meta-analysis of studies published could help to reduce the biases of single-phase II trials. Efficacy data were obtained on 636 patients. Pooled percentages of the overall response rate (ORR) and disease control rate (DCR) were 10% (95% CI: 6-15%, I2 = 67%, p < 0.1) and 42% (95% CI: 28-56%, I2 = 93%, p < 0.1), respectively. Median progression-free survival (mPFS) was 4.1 months (95% CI 2.6-5.4; I2 = 96%, p < 0.1) and median overall survival (mOS) was 11 months (95% CI 4.8-21.1; I2 = 98%, p < 0.1). Among the ICIs used as single agents, the anti-PD1 toripalimab achieved the highest ORR. Combination regimens were superior to monotherapy, e.g., the ICI combination nivolumab + ipilimumab, and the ICI + anti-angiogenetic combination atezolizumab + bevacizumab, both of which warrant further investigation. Promising efficacy and a good safety profile of ICIs represent a valid opportunity for expanding the therapeutic landscape of NENs. Predictive biomarkers are needed to identify the most suitable candidates for these regimens.
Keywords: PD-L1; PD1; immune checkpoint inhibitors; neuroendocrine tumors.