The expression of YAP1 in multiple lung malignancies therefore complicates the use of YAP1 expression to define a specific subtype of SCLC, particularly given the occurrence of combined tumors in which YAP1 expressing NSCLC may be admixed with SCLC, and the existence of YAP1-positive tumors that can mimic SCLC histologically, such as basaloid squamous cell carcinoma, poorly differentiated adenocarcinoma, high-grade adenoid cystic carcinoma, and SMARCA4-UT. The gene discussed is SMARCA4; the disease is adenoid cystic carcinoma.