CD274 and neoplasm: Additional biologic rationale for evaluating CPI in G3 NENs include their high rate of PD-L1 expression (ranging from 14% to 50% of tumours) and relatively high mutational load, compared to low-intermediate-grade NETs.31–33 A high mutational load is thought to increase the chances of immune recognition of neoantigens and may be associated with tumour responsiveness to CPI therapy.34 There are limited data on tumour mutation burden in G3 NENs but they frequently harbour multiple mutations in key oncogenic drivers.33,35