In the CIRCAN-NEC study [24], reporting on circulating tumour DNA (ctDNA) analysis in patients with advanced-stage GEP- or CUP-NEC, the most commonly mutated genes were TP53 and RB1, but also genes associated with GEP adenocarcinoma pathogenesis (e.g., KRAS, BRAF and APC). This evidence concerns the gene KRAS and neuroendocrine carcinoma.