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GENE-42. EXOME SEQUENCING ANALYSIS TO IDENTIFY POSSIBLE GENOMIC DRIVERS OF METASTATIC INVASION INTO THE SPINE


 The spine is a common site of metastatic spread of many cancers, causing debilitating pain and suffering. Treatment of spinal metastases is limited by resistance to radiation, chemotherapy, and proximity to the spinal cord. It is currently not known what causes the high incidence of spinal metastases, yet theories have been proposed, like the venous metastatic spread theory (Batson, 1940) and the “seed and soil” hypothesis (Paget, 1889), postulating that factors intrinsic to the tumor cells or to the microenvironment determine the location of cancer dissemination. Recent advances in high throughput sequencing allow for in depth analyses of the molecular signatures of tumors. To identify if there are intrinsic genetic alterations common to cancer cells that disseminate into the spine, we sequenced the exome of metastatic tumor cells harvested from the vertebrae of 9 patients with different primary tumors: carcinomas and sarcomas. Exome sequencing was performed using the HiSeq 4000 (Illumina) platform on DNA from tumor cell lines and control blood or bone marrow. Data was analyzed at the University of Michigan Bioinformatics Core and variants were called using the VarScan method (http://varscan.sourceforge.net/) in somatic mode. This analysis identified a total of 2366 genes with high impact mutations (888–1026 per sample); of these, 232 genes are common to all patients analyzed. Ninety-six of the identified genes (4%) are included in the Catalogue of Somatic Mutations in Cancer, and of these, seven: ACSL6, ACVR1, ALK, FGFR2, HSP90AA1, PTPN6 and PTPRB, have high impact mutations in all 9 patients with spinal metastatic disease. Pathway analysis of genes mutated in 5 or more patients shows significant overrepresentation of 41 KEGG pathways including TGFb, HIF1-a, VEGF, Wnt and Estrogen signaling pathways. Ongoing experiments are performed to validate the sequencing analysis and characterize functional consequences of the common mutations identified.