Research On Clonal Origin Of Gastric Mixed Adeno-neuroendocrine Carcinoma

Background:Gastric mixed adeno-neuroendocrine carcinoma(MANEC)is a rare primary gastric malignancy,named for its pathological characteristics of both adenocarcinoma and neuroendocrine carcinoma(NEC).Due to its low incidence,high heterogeneity,and lack of effective preclinical models,systematic studies on the molecular characteristics and clonal origin of it have not been conducted,and theoretical guidance for clinical treatment is also lacking.Therefore,exploring the multi-omic characteristics of gastric MANEC and compare its similarities and differences with gastric adenocarcinoma and gastric NEC at multiple levels,to provide a basis for subsequent research and treatment has become an urgent task for the study of this tumor.Methods:We screened patients with gastric MANEC who were surgically treated at Peking University Cancer Hospital from 2013 to 2019,and compared the prognosis with patients with gastric adenocarcinoma.Subsequently,we selected 5 FFPE samples of gastric MANEC,separated the two mixed components and analyzed the origin of the clone.We extracted DNA and mRNA from frozen samples for whole-exome and transcriptome sequencing,and compared them with gastric NEC and TCGA Asian gastric cancers in terms of mutation,copy number variation,tumor driver genes,tumor heterogeneity,and tumor stem cell characteristics.Finally,we take the gastric MANEC and the gastric NEC as a whole,and carry out molecular typing research through unsupervised clustering algorithm.Results:We found that the prognosis of gastric MANEC is worse than that of gastric adenocarcinoma,but is not significantly different from gastric NEC.Immunohistochemical analysis confirmed that the expression of Syn and CgA in gastric MANEC and gastric NEC is not statistically different.Phylogenetic tree showed that the two components in the mixed carcinoma shared a large number of driver gene mutations,presenting a typical branching evolution pattern.Mutation spectrum analysis showed that the two tumor components had a high similarity with gastric neuroendocrine carcinoma,which proved that both components in the mixed carcinoma were neuroendocrine origin.At the genomic level,gastric MANEC and gastric NEC have many similarities in high-frequency mutation genes and copy number variation but have great differences with gastric adenocarcinoma.In addition,high-frequency mutation of TP53 was detected in both gastric MANEC and gastric NEC,but the mutation rate of RBI was low in both,and VEGFA was greatly amplified in gastric MANEC.In the unsupervised cluster analysis of transcriptome hypervariable genes,most gastric MANECs and gastric NECs are clustered together,and only a few are clustered with gastric adenocarcinomas.Finally,gastric MANEC and gastric NEC were divided into EMT-associated type,high Myc-Her2 expression type,and high stemness.type.The three types have obvious characteristics and significant differences in prognosis.Conclusion:Gastric MANEC is of monoclonal origin,and is similar to gastric NEC at the prognosis,genome and transcriptome levels,and is quite different from gastric adenocarcinoma.TP53 has high frequency mutations in both gastric MANEC and gastric NEC,but the mutation rate of RBI is very low,which is obviously different from the reported NECs of other organs,and may be unique to gastric neuroendocrine tumors.In addition,VEGFA is highly amplified in gastric MANEC and may be a potential target for antiangiogenic therapy.Finally,The molecular classification of gastric MANECand gastric NEC may be an important reference for further research and treatment.