Impairment of endoxifen formation in tamoxifen-treated premenopausal breast cancer patients carrying reduced-function CYP2D6 alleles.
Br J Clin Pharmacol
; 87(3): 1243-1252, 2021 03.
Article
em En
| MEDLINE
| ID: mdl-32713032
ABSTRACT
AIMS:
Tamoxifen is bioactivated to endoxifen by polymorphic CYP2D6-dependent metabolism. Here, endoxifen levels were compared to CYP2D6 diplotypes, tentative target concentrations and side effects.METHODS:
In total, 118 Swedish premenopausal breast cancer patients diagnosed 2006-2014, with on-going postoperative tamoxifen treatment January 2017, were included. Biobanked DNA from peripheral blood was used for CYP2D6 genotyping by TaqMan real-time polymerase chain reaction (CYP2D6*1, *3, *4, *5, *6, *9, *10, *41, *1xN). Plasma levels of tamoxifen and 3 major metabolites were quantified by liquid chromatography-tandem mass spectrometry. Clinical information on treatment and side effects was retrospectively obtained from medical records.RESULTS:
In the final analysis of 114 patients, a clear relationship between CYP2D6 genotype and plasma endoxifen levels was evident. Low endoxifen (1.6-5.2 ng/mL), i.e. below the suggested threshold for clinical efficacy, was found in all patients with 2 reduced-function alleles, 2 null-alleles, or a null/reduced-function combination. CYP2D6*41 was the most common reduced-function allele (82%) and 17 of 21 CYP2D6*41-carriers exhibited a lower CYP2D6 activity than predicted from published guidelines. No difference in endoxifen levels was observed between carriers of 2 null-alleles vs patients homozygous for CYP2D6*41 or the corresponding heterozygous combination (P = .338). In patients with endoxifen levels <5.9 ng/mL (36/114), side effects were either mild or absent. At higher endoxifen levels moderate-to-severe side effects were reported in a concentration-dependent manner.CONCLUSION:
Significantly reduced endoxifen levels were observed not only in all homozygous carriers of CYP2D6 null-alleles, but also in carriers of 2 reduced-function alleles. This finding may be highly relevant for future, genotype-based dose considerations.Palavras-chave
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Neoplasias da Mama
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Citocromo P-450 CYP2D6
Tipo de estudo:
Guideline
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Observational_studies
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Prognostic_studies
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Risk_factors_studies
Limite:
Female
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Humans
Idioma:
En
Ano de publicação:
2021
Tipo de documento:
Article