The pyrimidine analog 5-fuorouracil (5-FU) is a cytostatic drug that is widely used for the treatment of many solid carcinomas including breast cancer. More than 80 – 85% of administered 5-FU is quickly metabolized in the liver through a series of metabolic steps involving an enzyme dihydropirimidine dehydrogenase (DPD). Patients with low DPD activity (approximately 2-4% of population) cannot effectively inactivate 5-FU which leads to high and sometimes even lethal toxicity. DPD is encoded by the DPYD gene. The mutant allele DPYD*2a is caused by a congenital mutation in the splicing sequence of intron 14 (IVS14+1G>A) of the DPYD gene. Patients with the IVS14+1G>A mutation produce a non-functional enzyme DPD and, when treated with 5-FU, toxic metabolites are accumulated in their bodies and it may lead to severe toxic reactions. Detection of the IVS14+1G>A mutation should be considered the important factor of toxicity prediction prior to the beginning of 5-FU therapy. In our study the IVS14+1G>A mutation was detected using the certified kit PGX-5FU Strip Assay (ViennaLab Diagnostics), which combines in vitro PCR and reversible hybridization. DNA was isolated from paraffin blocks, not from blood, which accelerated the whole process of diagnostic analysis. 40 female patients with histologically verified breast cancer (Grade I.-III.), who were treated in the Department of Oncology, (First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague), participated in this pilot study. DPYD genotyping was performed in all patients. One patient was a carrier of the IVS14+1G>A mutation in a heterozygous state and no patient was a carrier of homozygous mutation. On the basis of molecular analysis and symptom-atology the heterozygous patient received only a minimum effective dose of 5-FU.
 

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