Implementing a high-reliability, system-wide program for pre-emptive DPD deficiency testing for patients planned for a systemic fluoropyrimidine.

396 Background: Systemic fluoropyrimidine indications span several solid tumor types including gastrointestinal, breast, and head and neck malignancies. Dihydropyrimidine dehydrogenase (DPD) is the primary enzyme involved in fluoropyrimidine metabolism. Pathogenic polymorphisms of the gene encoding DPD (DPYD), occur at a rate of 4-7% and correlate with DPD enzyme deficiency. Failure to detect patients with DPD deficiency, and adjust the dosage preemptively, may result in severe toxicity, including death. Methods: Between December 2022 and May 2023, Dana-Farber Cancer Institute (DFCI) implemented a program across all sites of care to simplify and standardize preemptive DPYD testing for patient planned for a systemic fluoropyrimidine. The opt-out program includes an automated alert recommending DPYD testing when an oncologist orders a new regimen containing either 5FU or capecitabine, education for providers, pharmacists and nurses, patient education materials, standardized tracking of pending results, closed loop notification of providers of abnormal test results, dose adjustment guidelines, and patient tracking. DPYD allelic variants tested: *2A, *7, *8, *10, *13, rs67376798, rs75017182, rs115232898. Results: DPYD testing has increased from a baseline of 14% to 89%. Abnormal DPYD activity (score <2) has been detected in 5.1% of cases (28 of 553). 23 tests were performed preemptively and 5 reactively (all 5 after > grade 3 toxicity events). 27 cases had a single abnormal allele (activity score 1.5 or 1.0); a single case had 2 abnormal alleles (homozygous for rs75017182). Among 11 of the original 23 preemptively tested patients who continued fluoropyrimidine treatment at our facility, standardized dosage reductions were successfully applied for 10 (90.9%). None have experienced > grade 3 toxicity and subsequent dose escalation was possible for 5 (45.5%) patients. Conclusions: We have implemented a voluntary approach to facilitate routine preemptive DPYD testing for patients planned for a systemic fluoropyrimidine achieving an 89% usage rate. 28 of 553 (5.1%) patients were found to have at least a single allelic variant. Preemptive dose reductions were successfully applied for 90.9% of cases. The results provide proof of principle that pharmacogenomic testing can be applied in routine clinical practice and sets the stage for testing additional genes.