What are four phenotypes of tamoxifen metabolism?

Updated: Dec 07, 2018
  • Author: Maurie Markman, MD, MS; Chief Editor: Keith K Vaux, MD  more...
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The polymorphism has more than 100 known alleles, and based on genotype combinations, these are commonly classified into 4 phenotypes [10] :

  • Ultra-rapid metabolizers (UM)
  • Extensive (normal) metabolizers (EM)
  • Intermediate metabolizers (IM)
  • Poor metabolizers (PM) 

Prediction of an impaired tamoxifen metabolizer phenotype (IM, PM) with low endoxifen formation capacity is potentially important for personalized treatment decisions in breast cancer, such as increasing the therapeutic dose or replacing tamoxifen with an AI. [11]

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