Abstract 5887: Clonal heterogeneity and evolution of multifocal lung cancers revealed by whole exome sequencing to facilitate molecular diagnosis of multiple primary lung cancers
Authors: Liang Naixin , Bing Zhongxing , Song Yang , Wang Yadong , Wang Yanyu , Wu Pancheng , Jia Ziqi , Yang Xiaoying , Cao Lei , Cao Zhili , Yu Ruoying , Liu Rui , Ou Qiuxiang , Bao Hua , Wu Xue , Liu Peng , Zhang Shuyang , Li Shanqing 
Published: September 2020

Abstract
Background: Recent advances in CT screening of lung cancer has led to an increased incidence of detecting multifocal lung cancers (MFLCs). It has been suggested that the development of lung adenocarcinoma progresses from preinvasive atypical adenomatous hyperplasia (AAH) and adenocarcinoma in situ (AIS), to minimally invasive adenocarcinoma (MIA), and finally invasive lung adenocarcinoma (ADC). In patients with MFLCs, pulmonary nodules at different size and stage can be observed. Discrimination of synchronous multiple primary lung cancers (SMPLCs) from intrapulmonary metastases is challenging, which may influence the optimal approach for patient management.
Method:Whole-exome sequencing (WES) was performed on 100 resected lung nodule samples (18 AAH, 15 AIS, 12 MIA, 55 ADC) from 33 patients with clinical diagnosed SMPLCs (3 samples per patient in average, ranging from 1 to 8 samples per patient).
Result:In this cohort, 76% of patients (25/33) had at least one invasive ADC nodules while four patients had preinvasive (AAH/AIS) nodules only. Progressive evolution of lung tumors was marked by elevated chromosome instability (CIN) and tumor mutational burden (TMB). CIN was significantly higher in ADC lesions compared to other stage lesions. High frequencies of somatic copy number alterations (SCNAs) were identified in both arms of chr19 and the short arm of chr17 (17p) with a trend of progressively increase from AAH to ADC. Mutational signatures associated with age, APOBEC, BRAC and DNA mismatch repair (MMR) deficiency had the tendency to be enriched in later-stage nodules. 54.5% of the patients carried EGFR driver mutations, mainly L858R (89%), but the ratio of EGFR alterations displayed progressively increase from AAH (11%) to ADC (42%). Within the 29 patients with multiple nodules sampled, 10 cases displayed focal-specific EGFR-L858R, three of which had concurrent focal-specific EGFR-e19del. Five patients had EGFR-L858R detected in all the nodules. Pathway analysis revealed that dominant alterations along development of lung adenocarcinoma were centered around MAPK/ERK pathway, evolving from altered downstream genes, such as MAP2K1 and BRAF, in early stage to mutated upstream activator, such as EGFR, in later stage. Majority of MFLCs showed difference in clonal evolution and developmental stage, suggesting independent clonal origins. Multiple overlapping alterations were observed between intra-focal tumor lesions from the same or different lobes in 27.5% of patients (8/29), indicating intrapulmonary metastases.
Conclusion:
Evolution of lung tumors was associated with increased CIN, TMB, SCNV and altered MAPK/ERK pathway. Independent tumors with obviously molecular heterogeneity were revealed in majority of MFLCs while metastasis might exist. Patients with SMPLCs had the tendency to harbour shared EGFR driver L858R.
Citation Format: Naixin Liang, Zhongxing Bing, Yang Song, Yadong Wang, Yanyu Wang, Pancheng Wu, Ziqi Jia, Xiaoying Yang, Lei Cao, Zhili Cao, Ruoying Yu, Rui Liu, Qiuxiang Ou, Hua Bao, Xue Wu, Peng Liu, Shuyang Zhang, Shanqing Li. Clonal heterogeneity and evolution of multifocal lung cancers revealed by whole exome sequencing to facilitate molecular diagnosis of multiple primary lung cancers [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 5887.