Comprehensive investigation of mutational features of adenocarcinoma in situ and invasive adenocarcinoma among Chinese lung cancer patients.
Authors: Xiang Chan , Han Yuchen , Fang Wentao , Teng Haohua , Chen Shengnan , Guo Lianying , Shang Zhanxian , Zhao Jikai , Wei Jinzhi , Liu Jiaxin , Zhu Lei , Lizaso Analyn , Cai Yiran , Lin Jing , Yan Li 
Published: June 2021

9051 Background: Lung adenocarcinoma (LUAD) is further classified into several histological subtypes with adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), and invasive adenocarcinoma (IAC) as the three major subtypes according to the extent of invasion. AIS has been considered as a precursor of IAC. Considering the significantly higher mutation burden among IAC tumors than AIS tumors, it seems likely that AIS tumors undergo a process of accumulating various somatic mutations to gain invasive ability. To understand the gene mutations involved in this transformation, we compared the mutational features of AIS and IAC tumors. Methods: This retrospective study included 2,769 Chinese patients diagnosed with stage 0-IIIA LUAD. Targeted sequencing was performed on tissue DNA isolated from 246 AIS tumors and 2,523 IAC tumors using 68 lung cancer-related genes (Lung Core, Burning Rock Biotech). Results: Analysis of mutation profiles revealed that mutation count was significantly lower for AIS ( P< 0.01) as compared to IAC tumors. Moreover, AIS tumors had significantly higher mutation detection rates for ERBB2 exon 20 insertion (20ins) ( P≤0.05), EGFR 20ins ( P≤0.05), non-V600E BRAF mutations ( P≤0.05), and MAP2K1 small insertion-deletion variants ( P≤0.05). These 4 gene mutations were grouped and referred to as AIS-like mutations for further analysis. Detection rates of AIS-like mutations were 54.9% for AIS tumors and 7.8% for IAC tumors. Patients with AIS-like mutation-positive AIS tumors were significantly younger than those with AIS tumors without AIS-like mutations ( P =0.018), while age were similar for IAC tumors with or without AIS-like mutations. Mutation count was similar between AIS tumors with or without AIS-like mutations. Interestingly, IAC tumors harboring AIS-like mutations had a significantly higher mutation count than those harboring known oncogenic drivers ( P= 0.045). Further investigation of the molecular profiles of IAC tumors harboring AIS-like mutations (n = 198) revealed the presence of various concurrent mutations in 8 genes including TP53 (39.4%), EGFR (non-20ins) (16.7%), RB1 (7.1%), PIK3CA (6.6%), MET (5.1%), ROS1 (4.0%), FLT3 (4.0%), and PTEN (3.5%), which were absent among AIS tumors, particularly those that harbor AIS-like mutations. In addition to TP53 (35.8%), PIK3CA (4.5%), and RB1 (4.0%), IAC tumors without AIS-like mutations (n = 2,324) had additional concurrent mutations in 2 other genes CDK4 (5.7%) and STK11 (3.9%) as compared to AIS tumors. Conclusions: Our data suggest that AIS-like mutations could be involved in the early stages of tumorigenesis by initiating the accumulation of other gene mutations that are required for the transformation of AIS tumors into IAC tumors. Our study contributes to a deeper understanding of the distinct gene mutations between AIS and IAC tumors among Chinese LUAD patients.