3644 Background: Recent work has shown an association between longer survival and aspirin use in colorectal cancer (CRC) patients with mutated PIK3CA. It has been hypothesized that this survival advantage could occur via blocking the PI3K pathway and allowing apoptosis of mutated cancer cells. The goal of this work is examine the use of aspirin and outcome in CRC patients with PI3KCA mutation. Methods: PIK3CA mutation status was assessed in paraffin-embedded tumor samples from 471 CRC patients between 1998-2010. PIK3CA mutation was assessed by exome sequencing using an Illumina Next Generation (NGS) platform with 50-100X coverage on all patients. The BWA/GATK pipeline was used to identify variants and indels. Because matched normal samples were not available for comparison to identify somatic mutations, filtering of normal variants was performed using 1000 Genomes. The usage of aspirin was collected retrospectively with electronic chart review. Results: Out of 471 patients, 73 were found to have unique PI...