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Indications and consequences of MSI analysis in colorectal cancer

(2016) Lammertink, M.H.A. (Marieke)

Abstract (accepted as oral presentation at the autumn meeting of the Dutch Society of Gastroenterology, October 2016) Background: Microsatellite instability analysis (MSI) is a selection tool for genetic testing in patients that are suspected for Lynch syndrome (LS), based on the Bethesda criteria. The analysis is also performed to select patients who qualify for adjuvant chemotherapy when this concerns monotherapy with 5-fluoro-pyrimidine (5FU). Possible consequences of a positive test result are: (1) referral to a clinical geneticist, (2) impact on the type of surgery in case of young (<60 years) patients and (3) refrain from adjuvant chemotherapy. We studied the indications for MSI analysis and consequences of a positive test result. Methods: In a retrospective single center study we analysed all patients with colorectal cancer that were discussed in a multidisciplinary team between April 14th 2012 and January 1th 2016. Results: We included 660 patients. A total of 108 patients (16%) were tested for MSI. Indications for MSI analysis were: satisfying the Bethesda criteria n=53 (49%), selecting patients that may refrain from adjuvant chemotherapy n=40 (37%) and a rest group n=15 (mainly patients with a positive family history, not satisfying the Bethesda criteria). A total of 12 (11%) patients had MSI high tumors. Three of them (25%) were not referred for genetic counselling by accident. In one patient a germline MSH-6 mutation was identified. In 28 patients MSI was performed on tumor biopsies and available preoperatively. In three patients with MSI high tumors the type of surgery has not been changed. In three of 40 patients (8%) adjuvant chemotherapy was refrained because their tumors were MSI high. Conclusions: MSI analysis based on the Bethesda criteria revealed a germline mutation in 2% after DNA analysis. This did not influence the type of surgery but had consequences in the decision to treat with adjuvant chemotherapy in 8% of the patients. Consequences and practitioners responsibilities of MSI analysis should be part of the multidisciplinary CRC discussion as 25% of patients with MSI high tumors were not referred for genetic counseling





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