PGx tamoxifen

The status is determined by CYP2D6 genotyping (order panel identifier Panel00473). The assay interrogates the relevant CYP2D6 alleles and reports the resulting diplotype and the assigned metaboliser phenotype. The activity-score framework used to translate a diplotype into a phenotype is a maintained consensus that has been revised over time, so the current framework and any genotype-based guidance are held in the continuously maintained pharmacogenomic databases linked below rather than fixed on this page. Two interpretive limits apply: a normal or negative genotype reflects only the alleles tested and does not exclude reduced function from untested or poorly characterised variants; and, independently of genotype, phenoconversion by strong CYP2D6 inhibitors can make the functional (measured) status differ from the genotype-predicted phenotype.

• The result reports the patient’s constitutional CYP2D6 metaboliser status; it informs, but does not by itself dictate, therapeutic decisions, which remain with the treating physician.
• A genotype-based guideline for CYP2D6 and tamoxifen was published in 2018 and supports the relevance of CYP2D6 genotype to tamoxifen therapy. Its actionable dosing content is not reproduced here.
• The clinical utility of CYP2D6 genotyping for tamoxifen is contested. In contrast to the position, the state that study of CYP2D6 polymorphisms as a decision aid for adjuvant tamoxifen is not proven and should not be done in routine practice, and the association between CYP2D6 genotype and clinical outcome remains under debate.
• further advises that patients on tamoxifen avoid strong and moderate CYP2D6 inhibitors where possible.
• For current, actionable guidance consult the maintained databases: the CPIC gene page at and the PharmGKB gene resource at .

Content reviewed against the current guidelines on 24 July 2026. Pharmacogenomic classifications and dosing guidance are periodically revised; the linked databases above hold the day-current version.

• Goetz MP, Sangkuhl K, Guchelaar HJ, Schwab M, Province M, Whirl-Carrillo M, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 and tamoxifen therapy. Clin Pharmacol Ther. 2018;103(5):770-777. PMID: .
• Nofziger C, Turner AJ, Sangkuhl K, Whirl-Carrillo M, Agúndez JAG, Black JL, et al. PharmVar GeneFocus: CYP2D6. Clin Pharmacol Ther. 2020;107(1):154-170. PMID: .
• Caudle KE, Sangkuhl K, Whirl-Carrillo M, Swen JJ, Haidar CE, Klein TE, et al. Standardizing CYP2D6 genotype to phenotype translation: consensus recommendations from the Clinical Pharmacogenetics Implementation Consortium and Dutch Pharmacogenetics Working Group. Clin Transl Sci. 2020;13(1):116-124. PMID: .
• Loibl S, André F, Bachelot T, et al. Early breast cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Ann Oncol. 2024;35(2):159-182. PMID: .
• Cardoso F, Kyriakides S, Ohno S, Penault-Llorca F, Poortmans P, Rubio IT, et al. Early breast cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2019;30(8):1194-1220. PMID: .
• Mulder TAM, de With M, Del Re M, Danesi R, Mathijssen RHJ, van Schaik RHN. Clinical CYP2D6 genotyping to personalize adjuvant tamoxifen treatment in ER-positive breast cancer patients: current status of a controversy. Cancers (Basel). 2021;13(4):771. PMID: .