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). The gene discussed is RB1; the disease is adenocarcinoma.