Microsatellite instability testing in colorectal patients with Lynch syndrome: lessons learned from a case report and how to avoid such pitfalls.

Bowel cancer that has spread is a serious condition that will often lead to loss of life. There is a new treatment called immunotherapy which helps extend the life of people with cancer that has spread beyond the bowel, but it does not work for everyone. Immunotherapy works best for people whose tumors have lost the ability to repair DNA. People with Lynch syndrome often have these types of tumors because they are born with an inherited predisposition for faulty DNA repair. We treated a patient with Lynch syndrome and bowel cancer, and wanted to use immunotherapy, but the test we used failed to give the right result. We think this is because the test is not very good at picking up unusual types of mutations that can occur and that using another test as well will prevent this mistake from happening to others.