While both SCLC and SMARCA4-UT share high proliferative capacity (Ki67 positivity of 80–100%) and TP53 mutations, SMARCA4-UT tumors differ in their low TTF1 expression, lack of neuroendocrine markers, and high SMARCA4 mutation burden [37,39,40]. This evidence concerns the gene TP53 and small cell lung carcinoma.