Feasibility of implementing a pharmacist-led DPYD gene testing service for patients commencing 5-fluorouracil (5FU) or capecitabine.

Abstract

e18644 Background: Polymorphisms in the DPYD gene, which encodes for dihydropyrimidine dehydrogenase (DPD), may impair DPD metabolism of fluoropyrimidines (FP) and cause life-threatening toxicities. The European Medicines Agency (EMA) recommend testing for DPD activity before FP therapy, but the Australian Therapeutic Goods Administration and the US Food and Drug Administration do not currently recommend this. At our hospital, pre-emptive DPYD gene screening was established in response to 7 cases of severe FP-toxicity and significant challenges for timely access to the life-saving antidote, uridine triacetate (UT), in the preceding 3 years. This study assessed the feasibility of a pharmacist-led DPYD gene testing service in an Australian cancer centre. Methods: Patients planned for FP therapy, without previous FP exposure, were referred to the Clinical Pharmacogenetics (CPGx) pharmacist for consenting, before a blood or buccal swab sample was taken. An external genomics company screened for the five Clinical Pharmacogenetics Implementation Consortium (CPIC) recommended gene variants (c.1905+1G > A, c.1679T > G, c.2846A > T, c.1236G > A and c.557A > G). Dose recommendations based on CPIC guidelines and phenotype were made to the treating clinician. Patients were followed-up for toxicity (graded according to CTCAE v5.0) at 3-5 days post first FP exposure and pre-cycle 2. Results: Between 16 December 2019 and 11 December 2020, 311 patients were planned for FP therapy. Genetic testing did not occur for 13 patients, in the first two months of program implementation mostly due to unfamiliarity with procedures. Of the 298 genotyped patients (median age 59.5 years, 52.7% female, 67.8% Upper and Lower Gastrointestinal, 18.1% Breast), 274 (91.9%) were seen by the CPGx pharmacist within 1 day of referral. Median time from samples being taken to result availability was 6 days. 286 patient (96.0%) results were reported and acted upon prior to the planned cycle 1 FP commencement date. Overall, 1 patient (0.3%, 95%CI 0.1-1.9) was identified as a poor metaboliser and avoided FP therapy. Ten patients (3.4%, 95%CI 1.8-6.0) were identified as intermediate metabolisers, of which 2 patients did not receive chemotherapy due to changes in goals of care, 1 patient received only one cycle at 100% of the full dose but passed away due to disease progression, 1 patient required UT administration after cycle 2 despite 50% dose reductions for both cycles and 6 patients received an initial 50% dose reduction, where for subsequent cycles, 3 continued at this dose level, 2 had dose increases and 1 had a further dose reduction. 17 patients experienced at least one grade 3/4 toxicity pre-cycle 2; all had normal metaboliser phenotypes. Conclusions: A pharmacist-led DPYD gene testing service is feasible, with acceptable test result turnaround times and phenotype identification rates similar to that reported by the EMA.