Lethal 5-fluorouracil toxicity associated with a novel mutation in the dihydropyrimidine dehydrogenase gene

Abstract

5-Fluorouracil (5-FU) is one of the most commonly used chemotherapeutic agents for the systemic and palliative treatment of patients with cancers arising from the gastrointestinal tract, breast, head and neck. Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-FU; a DPD deficiency is increasingly being recognized as an important pharmacogenetic disorder in the etiology of severe 5-FU-associated toxicity. Recently, it has been shown that cancer patients who were genetically heterozygous or homozygous for a mutant allele of DPYD, the gene encoding DPD, suffered from severe toxicity, including death, following the administration of 5-FU [1, 2]. To date, 31 variant DPYD alleles have been identified in patients suffering from a (partial) DPD deficiency [1–3]. Considering the pivotal role of DPD in chemotherapy using 5-FU, the identification of novel mutations underlying a DPD deficiency is of utmost importance because it will allow the identification of patients at risk. Our patient was diagnosed at the age of 42 years with a stage II-C ovarian carcinoma and proved to be a carrier of a mutation in the BCRA-1 oncogene. Initial treatment consisted of carboplatin and paclitaxel. Upon relapse, she received intensive chemotherapy followed by a peripheral stem-cell transplantation, tamoxifen and chlorambucil. Four years after the initial diagnosis, palliative treatment with 5-FU and leucovorin was started due to the presence of symptomatic liver metastases. According to a once weekly bolus schedule, leucovorin (80 mg/m 2 ) was administered as a 1 h infusion followed by a short i.v. push of 5-FU (400 mg/m 2 ). Four days after this first single injection of 5-FU the patient developed a severe grade IV mucositis. At day 6, she developed a grade IV thrombopenia and a grade III anemia. A grade IV leucopenia, total alopecia, scaling and erythrodermia of the skin was observed 12 days later. Despite intensive treatment with i.v. antibiotics, fungostatics, reinfusion of peripheral stem cells (stored 24 months before) and supportive care, the patient developed infiltrative lesions in the lungs and died 21 days after the first push of 5-FU, with no signs of bone marrow recovery, continuing mucositis and total alopecia. Analysis of DPYD for the presence of mutations showed that the patient was heterozygous for a novel 61C→T nonsense mutation in exon 2, creating a translation stop codon (R21X). This nonsense mutation leads to premature termination of translation before the FAD and uracil/thymine binding sites and thus to a non-functional protein without any residual activity. In addition, the patient proved to be heterozygous for the IVS14+1G→A mutation. As a result, the mature DPD mRNA lacks a 165 nucleotide segment, corresponding to exon 14. Analysis of the coding region of DPYD showed that the patient was also heterozygous for two other mutations 1627A→G (I543V) and 85T→C (C29R), which have been suggested to be common polymorphisms. Considering the rapid onset of the lethal toxicity after the administration of 5-FU, it is highly likely that the two mutations 61C→T and IVS14+1G→A are located on different alleles, thus causing a complete deficiency of DPD. A high prevalence of the IVS14+1G→A mutation has been observed in the normal population with a frequency of heterozygotes of 1.8% [2]. Furthermore, the IVS14+1G→A mutation proved to be the most common mutation present among cancer patients with a partial DPD deficiency; it was detected in 50% of patients suffering from grade IV neutropenia [1, 4]. Recently, we showed that 90% of individuals heterozygous for a mutant DPYD allele has a DPD activity below the threshold value indicative of increased risk of 5-FU toxicity [4]. The important role of DPD in the etiology of 5-FU toxicity, therefore, warrants the analysis of DPD activity and genetic screening for DPYD mutations in cancer patients prior to the administration of 5-FU.