A neural network model trained on full CYP2D6 gene sequences increases the ability to predict CYP2D6-mediated tamoxifen metabolism.

Pre-therapeutic UGT1A1 genotyping is not yet routinely performed in most hospitals in patients starting irinotecan chemotherapy. The aim of this position paper was to evaluate the available evidence and to assess the potential value of genotyping of UGT1A1∗28 and UGT1A1*6 in patients before starting treatment with irinotecan to reduce the risk of severe toxicity. The literature was selected and assessed based on five pre-specified criteria: 1) the level of evidence for associations between UGT1A1 polymorphisms and irinotecan-induced severe toxicity, 2) clinical validity and utility of pre-therapeutic genotyping of UGT1A1, 3) safety and tolerability of irinotecan in carriers of UGT1A1 polymorphisms, 4) availability of specific dose recommendations for irinotecan in carriers of UGT1A1 polymorphisms, 5) evidence of cost benefits of pre-therapeutic genotyping of UGT1A1. On all five criteria, study results were favourable for pre-therapeutic genotyping of UGT1A1. A high level of evidence (level I) was found for a higher incidence of irinotecan-induced severe toxicity in homozygous carriers of UGT1A1*28 or UGT1A1*6. The clinical validity and utility of this genetic test proved to be acceptable. Dose-finding studies showed a lower maximum tolerated dose in homozygous variant allele carriers, and most of the drug labels and guidelines recommend a dose reduction of 25-30% in these patients. In addition, pre-therapeutic genotyping of UGT1A1 is likely to save costs. Pre-therapeutic genotyping of UGT1A1 in patients initiating treatment with irinotecan improves patient safety, is likely to be cost-saving, and should, therefore, become standard of care.

To determine the safety, feasibility, pharmacokinetics, and cost of UGT1A1 genotype-guided dosing of irinotecan. In this prospective, multicentre, non-randomised study, patients intended for treatment with irinotecan were pre-therapeutically genotyped for UGT1A1∗28 and UGT1A1∗93. Homozygous variant carriers (UGT1A1 poor metabolisers; PMs) received an initial 30% dose reduction. The primary endpoint was incidence of febrile neutropenia in the first two cycles of treatment. Toxicity in UGT1A1 PMs was compared to a historical cohort of UGT1A1 PMs treated with full dose therapy, and to UGT1A1 non-PMs treated with full dose therapy in the current study. Secondary endpoints were pharmacokinetics, feasibility, and costs. Of the 350 evaluable patients, 31 (8.9%) patients were UGT1A1 PM and received a median 30% dose reduction. The incidence of febrile neutropenia in this group was 6.5% compared to 24% in historical UGT1A1 PMs (P = 0.04) and was comparable to the incidence in UGT1A1 non-PMs treated with full dose therapy. Systemic exposure of SN-38 of reduced dosing in UGT1A1 PMs was still slightly higher compared to a standard-dosed irinotecan patient cohort (difference: +32%). Cost analysis showed that genotype-guided dosing was cost-saving with a cost reduction of €183 per patient. UGT1A1 genotype-guided dosing significantly reduces the incidence of febrile neutropenia in UGT1A1 PM patients treated with irinotecan, results in a therapeutically effective systemic drug exposure, and is cost-saving. Therefore, UGT1A1 genotype-guided dosing of irinotecan should be considered standard of care in order to improve individual patient safety.

PURPOSE: The Clinical Pharmacogenetics Implementation Consortium (CPIC) recommends screening for four common DPYD variants to prevent severe toxicity in patients with cancer treated with fluoropyrimidines. A 50% starting dose followed by toxicity-based dose titration is advised for patients heterozygous for these variants. In this study, the appropriateness of the CPIC-recommended 5-fluorouracil (5-FU) starting dose was evaluated. PATIENTS AND METHODS: Patients were grouped into four variant categories ( DPYD *2A [c.1905+1G>A], DPYD *13 [c.1679T>G], c.2846A>T [p.D949V], c.1236G>A/HapB3 [p.E412E]) and a DPYD wild-type control group. Uracil loading tests were used for phenotyping. Variant patients started on a 50% reduced 5-FU dose. On the basis of steady-state 5-FU plasma concentrations, dose adjustments were made during cycles 2-4 until an 5-FU target AUC _0-46h of 20-30 mg × h/L was achieved, if tolerated. RESULTS: Twenty-six wild-type controls and 34 DPYD variant patients were included: 16 with c.1236G>A/HapB3, eight with c.1905+1G>A, eight with p.D949V, and two with c.1679T>G. Heterozygous carriers of c.1905+1G>A ( DPYD *2A) and c.1679T>G ( DPYD* 13) displayed significant reduced uracil metabolism. The impact on uracil clearance was highly variable in p.D949V but only minor in c.1236G>A/HapB3 variants. In all, 65% of wild-type controls had 5-FU exposure within target range on a 100% dose (mean, 23.2; IQR, 6.6). In 97% of all variant patients, the 50% reduced dose resulted in 5-FU underexposure, with a median AUC of 10.6 mg × h/L (IQR, 3.2). Dose escalation to 70% or higher was tolerated in most patients, reaching the target AUC in 68% of patients. CONCLUSION: The current CPIC guidelines are overly conservative for c.1236G>A/HapB3 and most p.D949V variants. A 75% starting dose is more appropriate for most c.1236G>A/HapB3 carriers. We recommend 5-FU therapeutic drug monitoring in all patients with DPYD variants to achieve optimal 5-FU exposure.