CYP2D6-genotyping in the assessment of the effectiveness of therapy with tamoxifen in patients with advanced hormone receptor-positive breast cancer

Tamoxifen is a drug of choice for endocrine therapy of hormone receptor- positive breast cancer in women of reproductive age. The metabolic activity of tamoxifen is determined by the activity of the CYP2D6 enzyme encoded by the CYP2D6 gene: under the action of the enzyme, tamoxifen converts into the metabolically active form called endoxifen. Pharmacogenetic testing of the CYP2D6 gene in patients with hormone-positive breast cancer can help to predict response to therapy and assess the risk of side effects with the aim of improving long-term treatment outcomes.