LAUSR

759Background: Microsatellite instability (MSI) has been associated with improved survival outcomes in early stage CRC. In stage IV disease, MSI represents only 3-5% of cases and currently the prognostic implications are less clear. There is however evolving evidence that treatment pathways should include anti-PD-1 antibodies given the encouraging results in heavily pre-treated MSI mCRC patients. We undertook an analysis of the South Australian mCRC population based registry to explore the relevance of MSI status in this population based registry. Methods: The registry was analysed to assess patient characteristics and survival outcomes comparing patients with MSI or microsatellite stable (MSS) disease. K-M survival analysis was used to assess OS. Results: 4359 patients are registered on the data base. 598 (14%) patients had been tested for MSI. 62 (10.1%) of these patients had demonstrable MSI. Patient characteristics and outcomes are summarized in the table. There are statistically higher rates of right...