Rapid/warm autopsy to reveal APOBEC-mutagenesis as driver of heterogeneity of metastatic thoracic tumors.

Abstract

9023 Background: Intratumor heterogeneity has been characterized among multiple cancer types. In lung adenocarcinoma, APOBEC-mutagenesis has been shown to be a source of heterogeneity. However, these data are largely limited to early stage primary tumors. There is limited information about the role of APOBEC-mutagenesis and somatic variants, copy number changes, transcript and protein expression in influencing tumor heterogeneity in metastatic lung adenocarcinoma and other thoracic tumors. Methods: We applied whole exome sequencing, RNA-seq, OncoScan CNV and mass spectrometry-based proteomic analyses on 46 tumor regions from metastatic sites including lung, liver and kidney, obtained by rapid/warm autopsy from 4 patients (pts) with stage IV lung adenocarcinoma, 1 pt each with pleural mesothelioma and thymic carcinoma. The autopsy procedure was initiated between 2-4 hours of death. Results: All tumors displayed organ-specific, branched evolution that was consistent across exome, transcriptome and proteomic analyses. The degree of heterogeneity at the genomic and proteomic level was patient-specific. There was extensive heterogeneity within the tumors of one of four patients with lung adenocarcinoma and in the thymic carcinoma patient (both non-smokers) with multiple driver mutations and copy number changes occurring in only some of the tumors suggesting ongoing late tumor evolution. Further examination of the heterogenous thymic and lung adenocarcinoma tumors showed strong enrichment with the APOBEC-mutagenesis pattern and high associated levels of APOBEC3B mRNA. Conclusions: Metastatic lung adenocarcinoma, thymic carcinoma and mesothelioma evolve through a branched, organ-specific process with marked differences in the acquisition of significant driver mutations and copy number changes. APOBEC3B is a potential driver of heterogeneity in pts with advanced, heterogeneous metastatic lung adenocarcinoma and thymic carcinoma and needs to be evaluated further.