['Severe toxicity to 5-fluorouracil (5-FU) based chemotherapy in gastrointestinal cancer has been associated with constitutional genetic alterations of the dihydropyrimidine dehydrogenase gene (DPYD).', 'In this study, we evaluated DPYD promoter methylation through quantitative methylation-specific PCR and screened DPYD for large intragenic rearrangements in peripheral blood from 45 patients with gastrointestinal cancers who developed severe 5-FU toxicity. DPYD promoter methylation was also assessed in tumor tissue from 29 patients', 'Two cases with the IVS14+1G > A exon 14 skipping mutation (c.1905+1G > A), and one case carrying the 1845 G > T missense mutation (c.1845G > T) in the DPYD gene were identified. However, DPYD promoter methylation and large DPYD intragenic rearrangements were absent in all cases analyzed.'] Are promoter methylation and large intragenic rearrangements of DPYD implicated in severe toxicity to 5-fluorouracil-based chemotherapy in gastrointestinal cancer patients?