Excerpt

Testing tumours for deficient DNA mismatch repair (dMMR) has been identified as a practice that is potentially over-utilized. According to clinical experts, dMMR tumour testing appears to be transitioning from an approach aimed at identifying patients and families with Lynch syndrome (LS) into a tumour phenotyping procedure that can be used to predict the prognosis of colorectal cancer (CRC) and to guide for adjuvant chemotherapy decisions. The use of a test with a prognostic and predictive value falls under the realm of “personalized medicine.” According to oncology and pathology experts, this recent application of dMMR tumour testing is the major driver of new test requisitions. This transition has led to an increased demand for the test, with unclear benefits for the patient or family members. In general, there is a lack of clarity regarding when the tests should be ordered and the impact of tumour dMMR status on CRC outcomes in the current era of oxaliplatin- and irinotecan-based chemotherapy. The central question, however, is whether universal dMMR tumour testing of CRC tumours is a viable and desirable option, given the known limitations of LS pre-selection criteria based on age, history, and pathology, and recognizing the potential utility of tumour dMMR status for personalizing cancer therapy. Missed cases of LS resulting from a targeted tumour dMMR testing strategy that is restricted to pre-selected high-risk individuals (e.g., selected based on the rBG) can be problematic and costly for the system, which would potentially support broader (universal) dMMR tumour testing of all CRC tumours. Alternatively, universal tumour testing carries with it additional costs associated with testing all CRC patients, most of whom will not have LS.

In summary, there is uncertainty regarding:

1. Optimal eligibility criteria for dMMR tumour testing in:CRC patients to identify new families with LSCRC patients to inform prognosis or prediction of response to chemotherapy.
2. The cost-effectiveness of tumour screening strategies and algorithms in:CRC patients to identify new families with LSCRC patients to inform prognosis or prediction of response to chemotherapy.