Pharmacogenetic-guided dosing for fluoropyrimidine (DPYD) and irinotecan (UGT1A1*28) chemotherapies for patients with cancer (PACIFIC-PGx): A multicenter clinical trial

Abstract

PACIFIC-PGx evaluated the feasibility of implementing pharmacogenetics (PGx) screening in Australia and the impact of DPYD/UGT1A1 genotype-guided dosing on severe fluoropyrimidine (FP) and irinotecan-related toxicities and hospitalizations, compared to historical controls. This prospective single arm trial enrolled patients starting FP/irinotecan for any cancer between 7 January 2021 and 25 February 2022 from four Australian hospitals (one metropolitan, three regional). During the accrual period, 462/487 (95%) consecutive patients screened for eligibility for DPYD and 50/109 (46%) for UGT1A1 were enrolled and genotyped (feasibility analysis), with 276/462 (60%) for DPYD and 30/50 (60%) for UGT1A1 received FP/irinotecan (safety analysis). DPYD genotyping identified 96% (n = 443/462) Wild-Type, 4% (n = 19/462) Intermediate Metabolizers (50% dose reduction), and 0% Poor Metabolizers. UGT1A1 genotyping identified 52% (n = 26/50) Wild-Type, 40% (n = 20/50) heterozygous, and 8% (n = 4/50) homozygous (30% dose reduction). Key demographics for the FP/irinotecan safety cohorts included: age range 23-89/34-74 years, male 56%/73%, Caucasian 83%/73%, lower gastrointestinal cancer 50%/57%. Genotype results were reported prior to cycle-1 (96%), average 5-7 days from sample collection. PGx-dosing for DPYD variant allele carriers reduced high-grade toxicities compared to historic controls (7% vs. 39%; OR = 0.11, 95% CI 0.01-0.97, p = 0.024). High-grade toxicities among Wild-Type were similar (14% vs. 14%; OR = 0.99, 95% CI 0.64-1.54, p = 0.490). PGx-dosing reduced FP-related hospitalizations (-22%) and deaths (-3.7%) compared to controls. There were no high-grade toxicities or hospitalizations for UGT1A1*28 homozygotes. PGx screening and prescribing were feasible in routine oncology care and improved patient outcomes. Findings may inform expanded PGx programs within cancer and other disease settings.

FIGURE 1

(a) Trial profile: fluoropyrimidine patients. (b) Trial profile: irinotecan patients. (a) Historical control cohort from Froehlich et al. 2015. Out of 25 patients excluded, 11 patients may have had UGT1A1*28 tested if irinotecan treatment was confirmed. EOLC, end of life care; FP, fluoropyrimidines; WT, wild‐type. (b) IR, Irinotecan.

FIGURE 2

Odd ratio (OR) for high‐grade toxicity between DPYD variant allele carriers and wild‐type patients, and between PGx‐dosing (PACIFIC‐PGx) and standard dosing (HISTORIC control). Historical control cohort from Froehlich et al. 2015. Cl, confidence interval; OR, odds ratio; PGx, pharmacogenetics.

FIGURE 3

Forest plot of the multivariable analysis for high grade toxicity (grade 3 or 4) using COX Proportional Hazards Models for patients treated with fluoropyrimidines. GI, gastrointestinal.