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Why All Colorectal Cancer Patients Should Be Tested for MMR Deficiency


No two patients are the same when it comes to colorectal cancer care. And with so many available therapies, it is crucial for oncologists to gather all available information about their patient in order to make the best treatment recommendations. That’s why the National Comprehensive Cancer Network (NCCN) now recommends all colorectal cancer patients receive a genetic test called a Mismatch Repair (MMR) Deficiency test early on in treatment Although this test is considered the standard of care, most colorectal cancer patients do not get tested for MMR Deficiency, according to a new study from Fox Chase Cancer Center that was published in JAMA Oncology. Fox Chase Surgical Oncologist Nestor Esnaola, MD, MPH, MBA, FACS talked about why it’s important to start colorectal cancer treatment at a center that automatically performs this test.

What is MMR Deficiency?

Certain genes in the body, called MMR genes, have the ability to repair mismatches in DNA strands. Some people are born with mutations in these MMR genes and so, these DNA mismatches go unrepaired in some cases. DNA MMR deficiency is one of the best known and studied genetic causes of colorectal cancer.

It can impact treatment decisions and outcomes for colorectal cancer patients, and individuals and their family members who have this mutation may be at risk for additional cancers. MMR deficiency is estimated to affect as many as 15 percent of colorectal cancer patients and is also a characteristic feature of Lynch Syndrome, a hereditary disorder that can increase an individual’s risk of cancer.

The Benefits of Testing for MMR Deficiency

Esnaola said the MMR Deficiency Test also tells physicians whether they must develop a prevention and early detection plan to reduce a patient’s risk for subsequent cancers associated with Lynch Syndrome. “Furthermore MMR deficiency testing helps identify patients who may not benefit from certain types of chemotherapy, but may experience a benefit from immunotherapy,” Esnaola said. Still, an alarmingly low number of colorectal cancer patients are tested for MMR deficiency despite national guidelines suggesting every colorectal patient should be screened. Noncompliance with these guidelines is a pervasive problem that needs to be solved. 

Start Strong

At Fox Chase, MMR/MSI testing is performed automatically, Esnaola said, and suggested that this is the way forward. "Institutions that aim to optimize colorectal cancer care should implement reflexive testing," he said. Patients should be an active part of their treatment team and should be open to asking questions, even it means getting a second opinion. Not every medical center has these teams, or access to the latest technology like Fox Chase, so it’s important to start cancer treatment at a center that does.

Find out more about colorectal cancer treatment options at Fox Chase Cancer Center.