DR-143 Detection of microsatellite instability in metastatic colorectal cancer: the diagnostic accuracy of routine mismatch repair or microsatellite testing compared to whole genome sequencing.

The prognosis of patients with metastatic colorectal cancer is poor. Some of these patients are eligible for receiving potentially life-saving immunotherapy, but only if their tumor is classified as having microsatellite instability (MSI). Thus identifying these patients is important. The ability of the tests, that are used in routine medical practice, to correctly classify metastatic tumors as MSI is unclear. Comparing routine test results on MSI status, derived from the Dutch PALGA database, with MSI status based on whole genome sequencing, i.e. gold standard, using data from the Hartwig Medical Foundation, offers a unique opportunity to clarify this important issue.

Petur Snaebjornsson Netherlands Cancer Institute the Netherlands