Although recent findings have implicated DPYD in epithelial-to-mesenchymal transition (EMT) of breast cancer cells2, most interest in DPYD has stemmed from its role in limiting the bioavailability of the chemotherapeutic anti-metabolite 5-fluorouracil (5-FU) that exerts its therapeutic activity at least partly through anabolic uptake3–7. The gene discussed is DPYD; the disease is breast cancer.