A combination of pre-screening for DPD deficiency by genotyping/phenotyping methods and pharmacokinetics-guided dosing of 5-FU for precision treatment to prevent severe toxicity in gastrointestinal cancer patients.

Fluorouracil (5-FU) are broadly used in chemotherapeutic regimens for the
treatment of cancers. Dihydropyrimidine dehydrogenase (DPD) is a major enzyme
in the 5-FU metabolism pathway. Patients with a partial or complete DPD
deficiency have a strongly reduced capacity to metabolize 5-FU which may result
in severe or life-threatening toxicity when treated with a standard dose of
fluoropyrimidines. A partial DPD deficiency is present in 3-5% of the North
American and European population. DPD deficiency is most often caused by
genetic variants in the gene encoding DPD (DPYD). The four DPYD variants
considered most clinically relevant and with statistically significant
association with severe toxicity are DPYD*2A (rs3918290, c.1905+1G>A,
IVS14+1G>A), c.2846A>T (rs67376798, D949V), c.1679T>G (rs55886062, DPYD*13,
I560S), and c.1236G>A (rs56038477, E412E, in haplotype B3). Prospective
testing for DPD deficiency can prevent severe toxicity or mortality. Several
methods have been proposed for detection of DPD deficiency, based on either
genotyping of DPYD or measurement of the DPD phenotype. However, DPD deficiency
is not the only factor associated with variable concentrations of 5-FU. 5-FU
displays an exposure-response relationship between systemic exposure and
clinical events. Therapeutic Drug Monitoring (TDM) or pharmacokinetics
(PK)-guided dosing of 5-FU is also considered as an alternative to ensure an
acceptable exposure of 5-FU. Upfront DPD screening combined with PK guided 5-FU
dosing as a tool to personalize treatment has never been studied before. In
this study, we aim to investigate the PK of 5-FU for the 4 most common DPYD
genetic variants, in order to better define a safe starting dose for 5-FU in
DPD deficient patients.

The primary objective of this study is to investigate the clearance of 5-FU for
the 4 most common DPYD gene variants compared to the clearance of 5-FU in DPYD
wild-type patients. The secondary objectives of this study are to determine the
toxicity incidence and the extent of DPD deficiency as measured by Uracil
Loading Test (ULT) for the 4 most common DPYD variants, to evaluate the safety
and tolerability of reduced starting dose of 5-FU in patients with DPD
deficiency, to demonstrate the ability to achieve a target AUC range, to
establish that PK-guided 5-FU dosing decreases the incidence of 5-FU related
toxicities, to establish the sensitivity, specificity and predictive values of
the DPYD genotyping test and .to optimize the sampling moment of 5-FU in order
to minimize patient discomfort related to TDM procedures

The study is designed as a single-centre prospective inception cohort study.
All patients will be screened for DPD deficiency by DPYD genotyping and
separated into two groups; DPYD common variants and control group. Patients
with DPYD wild-type but who experience CTC grade 3-4 toxicity will also be
included in this study as a toxicity group. Patients will be tested with an
oral ULT to identify their DPD phenotype and measured an endogenous U/DHU
ratio. Therapeutic drug monitoring will be performed to follow-up patients*
5-FU plasma concentration after start chemotherapy treatment. 5-FU plasma
concentrations will be monitored until a steady state AUC of 20-30 mg.h/L is
reached or maximum 4 treatment cycles is reached.

5-FU dose adaptation according to the IATDMCT guideline.

The burden associated with participation:
Patients have to participate in this study for maximum 5 study visits.
Pre-screening: Physical examination and DPYD genotyping (1 blood sample (3 mL))
Visit ULT*: ULT + endogenous U/DHU ratio (3 blood samples, total 9 mL)
Visit 1**: 5-FU TDM (1 blood sample 3 mL; in PK subgroup in total 4 samples of
3 ml)
Visit 2**: 5-FU TDM (1 blood sample 3 mL; in PK subgroup in total 4 samples
of 3 ml)
Visit 3***: 5-FU TDM (1 blood sample 3 mL)
Visit 4***: 5-FU TDM (1 blood sample 3 mL)

* The ULT can be performed any time during the study, provided that there is at
least a 48 hr interval between the test and the previous or next chemotherapy
administration.
** A subgroup of 8-12 patients will be subject to additional blood sampling on
day 1 and day 2 of the first 2 treatment cycles. Three extra blood samples will
be drawn during continuous infusion of 5-FU.
*** As long as the target AUC has not yet been reached

The risk-benefit analysis:
The possible risks of this study are related to standard risk of venapunctures
and mild adverse reactions that might occur after uracil consumption during the
ULT procedure. The risk associated with extra blood sampling is minimal. The
results of the measurements will be used to individualise the chemotherapy dose
and add to improved patient safety.

Group relatedness:
5-FU based chemotherapy regimens are the first-line therapy for
gastrointestinal cancer patients. Therefore, this group of patients is related
to this study.