ARID1A and carcinoid tumor: NENs show site-specific molecular patterns: pulmonary large-cell NECs demonstrate FGF2 alterations; atypical carcinoids harbor KIT/PTEN/HNF1A/SMO variants; and GEP-NENs exhibit grade-dependent heterogeneity – low-grade tumors show ATRX/ARID1A/MEN1 aberrations while high-grade lesions display TP53/KRAS/APC alterations (14–16).