Background
Despite an extensive literature suggesting that high microsatellite instability (MSI-H) enhances survival and protects against recurrence after colorectal cancer (CRC) resection such effects remain controversial as many studies show no or only a weak bivariate association or no multivariable association. This study examined the association between MSI-H and recurrence and death due to CRC adjusting for death due to other cause as a competing risk.
Method
Data were drawn from a prospective hospital registry of consecutive resections for CRC, which contains detailed clinical, operative, pathology, adjuvant therapy and follow-up information. The cumulative incidence of recurrence and CRC-specific death were evaluated by competing risks regression.
Results
Among 1009 patients who had a resection between August 2002 and December 2008 and were followed to at least December 2013 there were 114 (11.3%) with MSI-H. After potentially curative resection and adjustment for 19 other prognostic variables and accounting for non-CRC death as a competing risk there was no association between MSI-H and recurrence (HR 0.8 95% CI 0.42-1.57) or CRC-specific death (HR 0.73 CI 0.39-1.35). For palliative resections there was no association between MSI-H and CRC-specific death (HR 0.65, CI 0.21-2.04). For both curative and palliative resections MSI-H had a bivariate association with non-CRC death (HR 1.55 CI 1.04-2.30 and HR3.80 CI 1.32-11.00 respectively) but this disappeared in multivariable models.
Conclusion
These results contradict the suggested protective association between MSI-H and recurrence or survival reported in other studies. MSI status may not be an independent prognostic variable for CRC.