Why Genetic Testing Matters for Patients with Gastrointestinal Cancers

Among patients with gastrointestinal cancers, genetic testing before chemotherapy may help improve patient safety by providing relevant information needed in order to customize treatment doses.

In a study published in JCO Precision Oncology, researchers at the Perelman School of Medicine at the University of Pennsylvania found that genetic testing before chemotherapy for gastrointestinal cancers may improve patient safety. The research showed that tailoring chemotherapy doses based on preemptive genetic testing cut side effects in half compared to patients with the same genetic variants who received a standard dose without being tested.

According to a news release from Penn Medicine, the study focused on variants in the DPYD and UGT1A1 genes, which affect how the body processes drugs.

"If you're being treated with a chemotherapy regimen that includes fluoropyrimidine, like 5-FU or capecitabine, or in combination with irinotecan, ask your physician for pharmacogenetic testing," said Sony Tuteja, the study's lead author.

Tuteja, who is also director of Pharmacogenomics at the Penn Medicine Center for Genomic Medicine and a research assistant professor of Translational Medicine and Human Genetics, explained that the testing isn't routinely done, but it is available and can reduce severe side effects.

Transcript

For patients with gastrointestinal cancers, what should be the big takeaway from this study?

If you’re being treated with a chemotherapy regimen that includes fluoropyrimidine, like 5-FU or capecitabine, or in combination with irinotecan, ask your physician for pharmacogenetic testing. It's not often done in clinical care because it's not well-incorporated into routine care, but it is available and can reduce severe toxicities.

These toxicities can be severe. They may be gastrointestinal in nature, causing diarrhea and vomiting, but can also lead to decreases in your white blood cell count that may result in serious infections. Other side effects can be hand-foot syndrome, which is a very painful shedding of the skin on your hands and feet, or mouth sores and mucositis.

In our study, we only captured those toxicities that resulted in visits to the emergency department, an oncology urgent care unit, or a hospitalization. So, we didn't even count the less severe toxicities that patients experience from chemotherapy. We really looked at severe toxicities that would result in one of those outcomes.

Transcript has been edited for clarity and conciseness.

Reference

1. “Genetic testing reduces risks from chemotherapy for gastrointestinal cancer patients,” by Penn Medicine. News release; Aug. 7, 2025. https://www.pennmedicine.org/news/genetic-testing-lowers-risks-from-chemo-for-gi-cancer

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