Adenosquamous carcinoma of the lung (ASC) is a rare subtype of non-small cell lung cancer, consisting of lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) components. ASC shows morphological characteristics of classic LUAD and LUSC but behaves more aggressively. Although ASC can serve as a model of lung cancer heterogeneity and transdifferentiation, its genomic background remains poorly understood. In this study, we sought to explore the genomic landscape of macrodissected LUAD and LUSC components of three ASC using whole exome sequencing (WES). Identified truncal mutations included the pan-cancer tumor-suppressor gene TP53 but also EGFR, BRAF, and MET, which are characteristic for LUAD but uncommon in LUSC. No truncal mutation of classical LUSC driver mutations were found. Both components showed unique driver mutations that did not overlap between the three ASC. Mutational signatures of truncal mutations differed from those of the branch mutations in their descendants LUAD and LUSC. Most common signatures were related to aging (1, 5) and smoking (4). Truncal chromosomal copy number aberrations shared by all three ASC included losses of 3p, 15q and 19p, and an amplified region in 5p. Furthermore, we detected loss of STK11 and SOX2 amplification in ASC, which has previously been shown to drive transdifferentiation from LUAD to LUSC in preclinical mouse models. Conclusively, this is the first study using WES to elucidate the clonal evolution of ASC. It provides strong evidence that the LUAD and LUSC components of ASC share a common origin and that the LUAD component appears to transform to LUSC.