show Abstracthide AbstractKaposi's sarcoma (KS), is an AIDS-associated neoplasm caused by the KS herpesvirus (KSHV). A mouse model of KSHV-dependent tumorigenicity, allowed us to induce KSHV viral-episome loss following tumor development to test the plausibility of “hit and run” mechanism by KSHV. RNA-seq-transcriptome analysis and CpG-methylation were performed on KSHV positive cells, KSHV positive tumors and tumors that developed following viral-episome loss. During KSHV tumorigenesis, hypo-methylation was detected of oncogenic and differentiation pathways. In contrast, during tumorigenesis following KSHV-episome loss, a tendency towards hyper-methylation was detected. We found the same set of innate-immunity related mutations undetected in KSHV-infected cells but present in all KSHV-positive tumors, indicating that pre-existing host mutations that provide an in vivo growth advantage are clonally-selected and contribute to KSHV-tumorigenesis. We found de novo mutations related to cell proliferation that, together with the PDGFRAD842V, were responsible for driving tumorigenesis in absence of the KSHV-episomes. Virally-induced irreversible genetic and epigenetic oncogenic alteration supports the possibility of “hit and run” KSHV-sarcomagenesis consistent with the existence of LANA-negative spindle-cells in KS lesions. Overall design: KSHV-infected KS lesions are composed of latently-infected cells, as well as cells expressing lytic genes that have been implicated in the development of the KS angioproliferative phenotype. The existence of KS lesions with varying levels of KSHV-infected cells suggests also the existence of virus-independent “hit and run” mechanisms of sarcomagenesis, whereby viral infection irreversibly induce genetic or epigenetic oncogenic alterations in host cells. We used the unique mECK36 animal model of multistep KSHV sarcomagenesis to dissect transcriptional, genetic and epigenetic mechanisms of KSHV direct and in-direct (“hit and run”) sarcomagenesis in an unbiased high-throughput fashion. These analyses revealed that KSHV in vivo tumorigenesis: A) Occurs predominantly with CpG hypo-methylation of oncogenic and differentiation pathways. B) Selects for pre-existing host mutations that allow the KSHV oncovirus to express the oncogenic lytic program by creating permissive environment for viral-induced innate immunity and inflammation, which provides a selective advantage in vivo conducive to tumorigenesis.