Wafik S. El-Deiry, MD, PhD, FACP
Deputy Cancer Center Director
Coleader, Molecular Therapeutics Program
William Wikoff Smith Chair in Cancer Research
Fox Chase Cancer Center
Genomic aberrations are becoming increasingly significant in the diagnosis and treatment of patients colorectal cancer (CRC), but the optimal timing and nature of the testing needed for these biomarkers is the subject of robust debate. Although testing for some genetic defects has been incorporated into the treatment paradigm, particularly for advanced disease, the clinical utility of up-front tumor sequencing that would yield wide-ranging information has not yet been established.
Mismatch Repair Deficiency
In the past several years, universal testing for mismatch repair deficiency (dMMR) has been adopted as a standard for all patients diagnosed with CRC. Tumor tissue is stained by immunohistochemistry (IHC) for mismatch repair (MMR) proteins. If these proteins are present, it is consistent with microsatellite stability (MSS) or a lack of dMMR. If there is loss of expression of MMR proteins, tumor DNA can be subjected to classical microsatellite instability (MSI) testing, which involves polymerase chain reaction amplification across a number of repetitive sequences found in the human genome.
DNA damage and repair pathways, and other DNA repair defects. When potentially actionable targets are identified for which therapeutics exist, patients can consider enrolling in open clinical trials (such as the NCI MATCH and ASCO TAPUR).
Growing Genomic Evidence
In 2017, our research team at Fox Chase Cancer Center in Philadelphia, Pennsylvania, reported that CRC tumors with dMMR have increased rates of BRCA2
mutations, as well as a higher frequency of activating EGFR
Although it remains unclear whether PARP inhibitors, anti-EGFR, or anti-NTRK therapeutics would be effective in dMMR tumors or add value if combined with immunotherapy in MSI-high tumors (those with biallelic BRCA2
mutations or activating mutations in EGFR
or the NTRK
genes), there is certainly compelling evidence that targeting activated NTRK
genes is effective.2
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