Clinical Relevance of Novel Polymorphisms in the Dihydropyrimidine Dehydrogenase (DPYD) Gene in Patients with Severe Fluoropyrimidine Toxicity: A Spanish Case-Control Study

Among cancer patients treated with fluoropyrimidines, 10–40% develop severe toxicity. Polymorphism of the dihydropyrimidine dehydrogenase (DPYD) gene may reduce DPD function, the main enzyme responsible for the metabolism of fluoropyrimidines. This leads to drug accumulation and to an increased risk of toxicity. Routine genotyping of this gene, which usually includes DPYD *HapB3, *2A, *13 and c.2846A > T (D949V) variants, helps predict approximately 20–30% of toxicity cases. For DPD intermediate (IM) or poor (PM) metabolizers, a dose adjustment or drug switch is warranted to avoid toxicity, respectively. Societies such as the Spanish Society of Pharmacogenetics and Pharmacogenomics (SEFF), the Dutch Pharmacogenetics Working Group (DPWG) or the Clinical Pharmacogenetics Implementation Consortium (CPIC) and regulatory agencies (e.g., the Spanish Medicines Agency, AEMPS) already recommend DPYD routine genotyping. However, the predictive capacity of genotyping is currently still limited. This can be explained by the presence of unknown polymorphisms affecting the function of the enzyme. In this case-control work, 11 cases of severe fluoropyrimidine toxicity in patients who did not carry any of the four variants mentioned above were matched with 22 controls, who did not develop toxicity and did not carry any variant. The DPYD exome was sequenced (Sanger) in search of potentially pathogenic mutations. DPYD rs367619008 (c.187 A > G, p.Lys63Glu), rs200643089 (c.2324 T > G, p.Leu775Trp) and rs76387818 (c.1084G > A, p.Val362Ile) increased the percentage of explained toxicities to 38–48%. Moreover, there was an intronic variant considered potentially pathogenic: rs944174134 (c.322-63G > A). Further studies are needed to confirm its clinical relevance. The remaining variants were considered non-pathogenic.

Sustainability and clinical outcomes of routine screening for pathogenic DPYD gene variants prior to fluoropyrimidine (FP) chemotherapy for gastrointestinal (GI) cancer.

216 Background: Dihyropyrimidine dehydrogenase (DPD) deficiency is present in 3-5% of patients, and is associated with substantially increased risk of severe and/or fatal toxicity during standard-dose FP chemotherapy. Genotyping of pathogenic DPYD variants is a readily available screening test for DPD deficiency, and prospective studies show that dose-reduced FP chemotherapy can be used safely in heterozygous DPYD variant carriers. Methods: Following a sentinel toxicity event the GI medical oncology group at the Norris Cotton Cancer Center adopted a shared practice of routine screening for pathogenic DPYD gene variants prior to FP chemotherapy (5-FU or capecitabine). Screening procedures involved physicians, NP/PAs, nurses, pharmacists, and schedulers. Testing was completed at a send-out lab until late 2020, when an in-house test became available. The current test panel evaluates for 3 gene variants: c.1905+1G > A (*2A), c.1679T > G (*13), and c.2846A > T. We report on the sustainability and clinical outcomes of DPYD gene variant screening. We identified all patients starting new FP-containing intravenous chemotherapy regimens (e.g., FOLFOX, CAPOX) for treatment of GI cancer at two sites (LEB & STJ) between Jan. 2019 and May 2021. We used electronic medical records to evaluate for completion of DPYD genotyping, and we describe the prevalence and management of DPYD gene variant carriers. Results: We identified 333 patients starting FP-containing chemotherapy regimens during the study period, including 287 patients without prior history of FP chemotherapy. Screening with DPYD genotyping was completed in 228 of 287 eligible patients (79%). Screening rates increased from 34% in Q1 of 2019 to 90% in Jan-May 2021. Five GI oncology sub-specialists accounted for 89% of screen-eligible patients and 96% of completed tests, but 10 unique physicians ordered ≥1 test. Of 228 screened patients, six (2.6%) were heterozygous carriers of pathogenic DPYD gene variants (*2A [2 patients], *13 [1], and c.2846A > T [3]). Variant carriers started FP chemotherapy with a 33-50% reduction. Two of six patients required further dose reduction due to FP-related toxicity (grade 4 neutropenia, grade 3 diarrhea). All evaluable variant carriers completed planned initial treatment. Implementation challenges included variable insurance coverage of DPYD genotyping, site-specific test ordering and reporting processes, and inconsistent turn-around time for send-out testing (resolved with on-site testing). Conclusions: Routine screening for pathogenic DPYD gene variants prior to FP chemotherapy is feasible and sustainable in the U.S. DPYD genotyping coupled with chemotherapy dose reductions for DPYD variant carriers facilitates safe and timely completion of planned chemotherapy treatments.

Fluoropyrimidine-Induced Severe Toxicities Associated with Rare DPYD Polymorphisms: Case Series from Saudi Arabia and a Review of the Literature

Dihydropyrimidine dehydrogenase (DPD) is the major enzyme in the catabolism of 5-Fluorouracil (5-FU) and its prodrug capecitabine. We report cases from our institute with colorectal cancer who experienced severe toxicities to standard dose 5-FU based chemotherapy. DPYD gene sequencing revealed rare different polymorphisms that prompted dose adjustments of administered 5-FU and capecitabine. To our knowledge, this is the first case series looking at DPYD polymorphisms in the Saudi Arabian population.

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

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.

Cost effectiveness of DPYD genotyping to screen for dihydropyrimidine dehydrogenase (DPD) deficiency prior to adjuvant chemotherapy for colon cancer.

55 Background: Fluoropyrimidine chemotherapy agents, including 5-fluorouracil and capecitabine, are the backbone of adjuvant treatment for colon cancer, and adjuvant chemotherapy substantially reduces recurrence and mortality after surgical resection of stage 3 colon cancer. While fluoropyrimidine chemotherapy is generally safe, the risk of severe, potentially fatal chemotherapy toxicity is substantially increased for the 2-3% of U.S. patients with DPD deficiency caused by pathogenic variants in the DPYD gene. DPYD genotype testing is readily available in the U.S. but has not been widely adopted. We evaluated the cost effectiveness of DPYD genotyping prior to adjuvant chemotherapy for colon cancer in the U.S. Methods: We constructed a Markov model to simulate screening for DPD deficiency with DPYD genotyping (versus no screening) among patients receiving fluoropyrimidine-based adjuvant chemotherapy for stage 3 colon cancer. Screen-positive patients were modeled to receive dose-reduced fluoropyrimidine chemotherapy. Model transition probabilities for treatment-related toxicities were derived from published clinical trial data with annotation of DPYD genotype and chemotherapy dosing strategy. Our analysis is from the healthcare perspective, with a time horizon of five years and an annual discount rate of 3% for future costs and benefits. Direct healthcare costs and health utilities were estimated from published sources and converted to 2020 US dollars, and post-treatment survival was modeled from SEER data. The primary outcome was the incremental cost-effectiveness ratio (ICER), defined as dollars per quality-adjusted life year (QALY). We used a value of $100,000/QALY as the cost-effectiveness threshold. One-way sensitivity analyses were used to examine model uncertainty. Results: Compared with no screening, screening for DPD deficiency with DPYD genotyping increased per-patient costs by $106 and improved quality-adjusted survival by 0.0028 QALYs, leading to an ICER of $37,300/QALY. In one-way sensitivity analyses, the ICER exceeded $100,000/QALY when the carrier frequency of pathogenic DPYD gene variants was less than 1.17%, and when the specificity of DPYD genotyping was less than 98.9%. Cost-effectiveness estimates were not sensitive to the cost of DPYD genotyping, the cost of toxicity-related hospitalizations, or the health utility associated with grade 3-4 toxicity. Conclusions: Among patients receiving adjuvant chemotherapy for stage 3 colon cancer, screening for DPD deficiency with DPYD genotyping is a cost-effective strategy for preventing infrequent but severe, sometimes fatal toxicities of fluoropyrimidine chemotherapy.

Near Miss or Standard of Care? DPYD Screening for Cancer Patients Receiving Fluorouracil

5-fluorouracil (5-FU) and its pro-drug capecitabine are widely used anticancer agents. Most 5-FU catabolism is dependent on dihydropyrimidine dehydrogenase (DPD) encoded by the DPYD gene, and DPYD variants that reduce DPD function increase 5-FU toxicity. Most DPD deficient patients are heterozygous and can be treated with reduced 5-FU dosing. We describe a patient with a genotype associated with near complete absence of DPD function, and severe and likely fatal toxicity with 5-FU treatment. The patient was treated effectively with alternative systemic therapy. Routine pretreatment DPYD genotyping is recommended by the European Medicines Agency, and guidelines for use of 5-FU in DPD deficient patients are available. However, outside the province of Quebec, routine pretreatment screening for DPD deficiency remains unavailable in Canada. It is likely our patient would have died from 5-FU toxicity under the current standard of care, but instead provides an example of the potential benefit of DPYD screening on patient outcomes.

All You Need to Know About DPYD Genetic Testing for Patients Treated With Fluorouracil and Capecitabine: A Practitioner-Friendly Guide

Fluoropyrimidines (fluorouracil, capecitabine, and other analogs) are highly used anticancer drugs worldwide. However, patients with cancer treated with these drugs might experience severe, life-threatening toxicity because of germline genetic variation in the DPYD gene. This is a genetic predisposition with an established mechanistic basis that links genetic variation in the DPYD gene to an increase in systemic drug exposure, resulting in an increased risk of toxicity. Pharmacology guidelines provide recommendations on avoiding treatment with fluoropyrimidines or reducing their dose in patients carrying DPYD genetic variants conferring an increased risk of toxicity. However, oncology societies in the United States do not recommend systematic testing. Instead, on April 30, 2020, the European Society for Medical Oncology issued a document recommending genetic testing. In this scenario of contradicting information, practicing oncologists struggle with reaching an informed decision on whether genetic testing should be applied before treatment. This is mostly due to uncertainty about the clinical relevance of genetic testing from the perspective of a practicing oncologist. To reach an informed decision, practicing oncologists need access to concise information on the genetic variants to be tested and a practitioner-friendly interpretation of the test results. We believe this information is currently lacking. To our knowledge, for the first time, we provide a single guide for health care professionals to make an evidence-based decision about DPYD testing for patients with cancer. This article provides the essential knowledge base for oncologists to have an informed discussion with their patients about the genetic testing for DPYD. This document assists practitioners in quickly evaluating whether, when, where, and how to order a DPYD genetic test.