Pre-therapeutic dihydropyridimidine dehydrogenase (DPD) deficiency screening: Impact on fluoropyrimidine dose reduction at the second chemotherapy cycle and on early severe toxicity.

3096 Background: DPD deficiency screening before fluoropyrimidine is a matter of debate. To avoid lethal toxicity, French authorities impose DPD screening before fluoropyrimidine-based chemotherapy by dosing uracilemia since April 2019. Methods: We have included all consecutive adult patients receiving 5-fluorouracil (5-FU) or capecitabin from April 2019 to January 2020 in 6 cancer centers. During the study period, different methods for screening had been applied: DPYD complete sequencing, phenotype (uracilemia and/or dihydrouracilemia/uracilemia ratio - UH2/U -) or both. All sceening tests were conducted in the same laboratory. Association between the method of DPD screening and fluoropyrimidine dose reduction at second chemotherapy cycle or on severe ≥grade 3 early toxicity (between first and second cycle) was evaluated using multivariate logistic regression. Concordance between genotype and phenotype for DPD deficiency was explored using Cohen Kappa test. Results: We included 597 patients, the median age was 63 (range, 55-77). The most prevalent cancers were digestive (68.3%), head and neck (19.4%) and breast (9.2%). 12.3% of patients received capecitabine and 87.3% received polychemotherapy. DPD deficiency screening was done for most of patients (n=519, 86.9%). DPD screening method consisted in full sequencing of DPYP (n=41; 7.9%), phenotype analysis (n=44, 8.5%) or both (n=424, 83.6%). We did not identify any complete DPD deficiency. Uracilemia was dosed for 467 patients, the median was 6.5 ng/mL and for 21 patients (4.5%) uracilemia was > 16 ng/mL and/or UH2/U <6, suggesting DPD deficiency. Severe early toxicities were observed for 82 patients (14%), with two patients presenting grade 5 toxicity. Overall DPD screening and method of DPD screening were not associated with fluoropyrimidine dose reduction at second cycle or early severe toxicity. In multivariate analysis, the only predictor for fluoropyrimidine reduction at second cycle (n = 125 patients) was polychemotherapy (OR=2.8; p=0.012). Kappa between uracilemia and UH2/U was 0.23 (poor concordance). Kappa between DPYP sequencing and uracilemia or UH2/U was 0.09 (very poor concordance). Conclusions: No DPD deficiency screening method was associated with dose adaptation at second cycle or early severe toxicity. The optimal strategy for DPD screening requires further clinical evaluation.