Page 153 - Personalised medicine of fluoropyrimidines using DPYD pharmacogenetics Carin Lunenburg

Safety analysis on DPYD genotype-guided dosing
and each new cycle according to routine clinical care, for evaluation of treatment safety.
DPYD genotyping
Genotyping of the four DPYD variants DPYD*2A, c.2846A>T, c.1679T>G and c.1236G>A was performed before start of treatment. Genotyping was performed in a clinical laboratory of the local hospital or in one of the other participating centers of this trial. Validated assays were used and all laboratories participated in a Dutch national proficiency testing program for all four DPYD variants.19
Pharmacokinetics and DPD enzyme activity 5 In DPYD variant allele carriers who provided written informed consent for additional tests, plasma levels of capecitabine, 5-FU, and their metabolites were determined at the first day
of a capecitabine/5-FU cycle (preferably the first cycle) to assess the pharmacokinetic profile
in these patients. A validated ultra-performance liquid chromatography tandem mass- spectrometry (UPLC-MS/MS) method was used (details in the Supplementary methods). Results of pharmacokinetic parameters, including the area under the plasma concentration- time curve (AUC) and half-life (t1/2) were calculated using non-compartmental analysis, and compared to control values derived from literature.20
DPD enzyme activity in peripheral blood mononuclear cells (PBMCs) was determined in a pretreatment sample in the DPYD variant allele carriers and compared to DPD enzyme activity measured in wild-type patients in this study, using a validated assay.21
Outcomes
The primary endpoint of the study was the frequency of severe overall fluoropyrimidine- related toxicity across the entire treatment duration. A comparison was made between the incidence of severe toxicity in DPYD variant allele carriers treated with reduced dose and in wild-type patients treated with standard dose in this study. In addition to this, the relative risk for severe toxicity of these DPYD variant allele carriers treated with reduced dose compared to non-carriers in the study was calculated. A comparison between this calculated relative risk and a similarly calculated relative risk for DPYD variant allele carriers treated with full dose in a historical cohort derived from a previously published meta-analysis10 was made. Secondary endpoints included pharmacokinetics of capecitabine and 5-FU in DPYD variant allele carriers and measurements of DPD enzyme activity. Another secondary endpoint was a cost analysis on individualized dosing based on upfront DPYD genotyping, of which results will be reported separately.
Statistical analysis
The sample size was based on a one stage A’Hern (phase II) design22 and calculated under the assumption that overall fluoropyrimidine-related severe toxicity could be reduced from 60% (in DPYD variant allele carriers receiving standard dose)10,15 to 20% by individualized dosing in DPYD variant allele carriers. This resulted in a required sample size of eleven variant carriers. To reach this number of variant carriers, we used a single DPYD variant (c.2846A>T, assumed variant frequency of 1%) to calculate the total sample size, resulting in
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