CTNNB1 and neuroendocrine carcinoma: The second most frequently mutated gene in TCS is CTNNB1, encoding β-catenin [18,19,20,22] and frequently co-occurring with SMARCA4 mutations in TCS and in SMARCA4-deficient carcinoma, olfactory carcinoma and neuroendocrine carcinomas [25,40,42,43,44,45,48,49].