Gastroesophageal adenocarcinoma (GEA) is a leading cause of cancer-related death worldwide with a five-year survival rate of less than twenty percent. The development of peritoneal metastasis (PM) is the most common progression of GEA and leads to an exceptionally poor prognosis with a median survival rate of less than four months. This poor prognosis results from the late presentation of the disease, the inability to surgically resect the cancerous lesions and the absence of therapeutic options. The lack of actionable target genes involved in the progression of GEA has made it difficult to understand and treat its progression. Through deep whole exome sequencing of five patient-matched primary GEA tumors, peritoneal metastases and adjacent normal tissues (n=15), we have discovered an enrichment of somatic mutations within several known cancer genes previously reported to be involved in cancer progression and metastasis, such as CDH1 and MYH9