FDA Update Reflects Need for Genetic Testing Prior to Capecitabine
Advocating for Genetic Testing Before 5-FU or Capecitabine
At the 2026 American Society of Clinical Oncology Gastrointestinal Cancers Symposium, Vimal Scott Kapoor, MD, BSc, MSc, of University of Toronto, met with Karen Merritt, co-founder of Advocates for Universal DPD/DPYD Testing, about the need for DPYD testing prior to treatment with fluoropyrimidine chemotherapies.
Fluoropyrimidines, including fluorouracil (5-FU) and capecitabine, an oral form of 5-FU, are commonly used in the treatment of several gastrointestinal cancers. The enzyme dihydropyrimidine dehydrogenase (DPD), which is the primary metabolizer for 5-FU, is encoded by the DPYD gene. Certain DPYD mutations can result in loss of DPD activity, and patients with DPD deficiency treated with 5-FU or capecitabine may have an increased risk of serious, potentially fatal adverse events.
Advocates for Universal DPD/DPYD Testing was founded to push for pretreatment DPYD screening to be added to prescribing information and treatment guidelines in the United States to avoid preventable deaths because of unknown DPD deficiency. Pretreatment DPD screening has been standard in other countries around the world for many years, said Dr. Kapoor.
In October 2025, the FDA updated the boxed warning on capecitabine’s prescribing information to recommend testing for genetic variants of DPYD before starting capecitabine. The National Comprehensive Cancer Network also updated treatment guidelines for 5-FU and capecitabine in colon cancer. These updates reflect growing acknowledgement of testing for DPD deficiency, and will hopefully be followed by more treatment label and guideline updates, said Ms. Merritt.