NBN and neoplasm: In this report, we describe a patient with PACC whose tumor harbored both an activating SEL1L::NTRK1 fusion and somatic biallelic inactivation of NBN. Upon disease progression on treatment with folinic acid, fluorouracil, irinotecan, and oxaliplatin (FOLFIRINOX), a novel reversion mutation restoring the NBN reading frame was detected, suggesting a potential link between NBN LOF, PACC progression, and the evolution of therapeutic resistance to mainstay treatment.