American Board of Internal Medicine (ABIM) Certification Practice Exam

What does MMR deficiency testing help to rule out in colorectal cancer patients?

1. Familial adenomatous polyposis

2. Peutz-Jeghers syndrome

3. Lynch syndrome

4. Colon inflammatory disease

The correct answer is: Lynch syndrome

MMR (mismatch repair) deficiency testing is primarily used in the context of colorectal cancer to identify Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer (HNPCC). Lynch syndrome is characterized by an increased risk of colorectal cancer and other associated malignancies due to inherited defects in the mismatch repair genes. When MMR deficiency testing is performed, it helps to determine whether a colorectal tumor exhibits characteristics consistent with these genetic defects. If a patient’s tumor shows MMR deficiency, it indicates a higher probability they have Lynch syndrome, and further genetic counseling and testing may be warranted for the patient and family members. In contrast, the other options involve different genetic mechanisms or conditions that are not indicated by MMR deficiency testing. Familial adenomatous polyposis and Peutz-Jeghers syndrome are both syndromic conditions linked to distinct genetic mutations, specifically APC and STK11 respectively, which are unrelated to the mismatch repair system. Colon inflammatory disease does not relate to MMR status either, as it pertains more to non-genetic factors affecting the colon. Thus, MMR deficiency testing is a crucial tool for identifying those patients who may have Lynch syndrome, leading to appropriate management strategies.