Informed decisions regarding microsatellite instability testing: need for an intention-to-screen analysis

informed consent on microsatellite instability (MSI) testing in patients with colorectal cancer (CRC) who have suspected Lynch syndrome met the primary end point: a CD-ROM–assisted intervention had a positive impact on the education of patients. However, in our opinion, the authors’ conclusions on the secondary outcomes suffer from a substantial selection bias. They suggest that decisional and emotional distress were negligible among patients who accepted to be randomly assigned, which ignores that more than one third of patients denied participation in the study. Although this regards secondary end points, it is relevant for medical oncologists, because it pertains to daily practice. We think that the logical hierarchy of the issues related to advising patients with CRC about MSI testing is as follows: whether to do that; when to do that; who should do that; and how to do that. Testing for MSI is becoming more and more popular. Some experts suggest to perform universal MSI testing on all patients with newly diagnosed CRC, regardless of age and family history. 2 This is because regular surveillance is of clinical benefit for relatives at risk. 3 In contrast, the benefit of such testing for individual patients with CRC has not been definitively proven: the type of surgery and chemotherapy are the same for patients with sporadic and Lynch syndrome CRC, 4 but the follow-up may be different (ie, the issue of whether to do that). Mastering the clinical implications of MSI testing and sharing them with our patients constitute prohibitive challenges for the oncologists. The patients themselves, who often want to concentrate on the treatment of their cancer, present a challenge as well (ie, the issues of when and who). Recent guidelines and policy statements from both the United