Abstract 1493: The clonal relationship between adenomatous and squamous components in adenosquamous carcinoma of the lung

Background: Adenosquamous carcinoma (ASC) is a rare dichotomous malignancy of non-small-cell lung cancer (NSCLC) consisting of lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) components. Although ASC has morphologically distinct characteristics of LUAD and LUSC, it behaves more aggressively than either subtype alone and is associated with worse prognosis. To date, not much is known about the molecular makeup of this tumor. In this study, we performed whole exome sequencing to investigate the evolutionary and clonal relationship between the two components of ASC. Methods: FFPE tissues of three ASCs were examined. After staining with the lineage markers TTF-1 and p40 to visualize LUAD and LUSC, respectively, the two components were macrodissected and subjected to whole exome sequencing separately. Results: The six separately analyzed tumor areas harbored a median of 73 (range 54 - 255) non-synonymous somatic mutations and a median mutation burden of 3.5 mutations/Mb (range 2.3 - 11.6). The LUSC and LUAD components of the three ASCs shared 46 - 299 mutations, accounting for 45%-87% of the mutations. Clonality analysis shows that most of driver mutations were clonal, further supporting the monoclonal origin of the two components. We detected 19 shared cancer gene mutations including TP53 p.Gln192* and p.His179Arg. An additional TP53 mutation p.Gly108Asp was found in LUAD of one patient. We further identified truncal mutations in EGFR, BRAF and MET, which are characteristic for LUAD but uncommon in LUSC. Furthermore,AMER1 and KMT2D, present in 9% and 12% of LUAD patients but not yet described in LUSC, were truncally mutated in two patients. No truncal mutations were found in typical LUSC driver genes such as FAT1 or PTEN. Shared chromosomal copy number aberrations between the two components were detected in all patients and included losses of 3p, 15q and 19p, and an amplified region in 5p, encompassing TERT. Focal deletions that occurred in all samples, such as in chromosome 3p are common in both classical LUAD and LUSC, whereas deletion in 15q and 19p occur in >90% of LUAD but in only 20% of LUSC. Identification of genomic SOX2amplification and STK11 loss in two of the three LUSC components, each, support previous pre-clinical evidence from mouse models suggesting a role of these genes in transdifferentiation from LUSC to ASC. Phylogenetic and mutational signature analyses showed that the trunks of all three ASCs were dominated by ageing and smoking-related signatures 1 and 4. However, the contributions of signatures changed markedly in the LUAD and LUSC branches. Conclusion: Our study investigated two macrodissected components, LUAD and LUSC, from three patients with ASC. Shared mutations and copy number aberrations suggested a LUAD-like genetic profile and demonstrated a clear monoclonal relationship between the two components indicative of a common ancestor. However, there were also major differences between the distinct components representing diverse evolutionary trajectories. Citation Format: Luca Roma, Arthur Krause, Salvatore Piscuoglio, Charlotte K. Ng, Lukas Bubendorf. The clonal relationship between adenomatous and squamous components in adenosquamous carcinoma of the lung [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1493.