Statement: The Ultra-rapid Metabolizers group of the primary trial had average increase of Endoxifen Concentration over 6 mg/m2 over 4 months.
Primary_evidence: Outcome Measurement:    Endoxifen Concentrations in Participants Receiving Tamoxifen Citrate Dose of 20 mg or 40 mg Stratified by the Metabolizing CYP2D6 Genotypes   Measurements of plasma concentrations of the key active metabolite of tamoxifen, endoxifen, were measured at baseline and after 4 months of treatment; The most common CYP2D6 alleles have been grouped by functional activity classifications with descending activity: ultra-rapid (UM), extensive (EM), intermediate (IM) or poor (PM) metabolism. A given patient has two alleles, giving them 10 possible allelic combinations, or diplotypes (UM/UM, UM/EM, EM/EM, etc.). These diplotypes are collapsed into four phenotypes, UM, EM, IM or PM.   Time frame: 4 months Results 1:    Arm/Group Title: Ultra-rapid Metabolizers   Arm/Group Description: Those with the highest transformation of the CYP2D6 genotype to allelic activity   Overall Number of Participants Analyzed: 5   Mean (Standard Deviation)   Unit of Measure: ng/mL  Baseline endoxifen concentration: 5 participants   8.4         (4.59)   4-Month endoxifen concentration: 4 participants   15.35         (5.48) Results 2:    Arm/Group Title: Extensive Metabolizers   Arm/Group Description: Those with the most normal transformation of the CYP2D6 genotype to allelic activity   Overall Number of Participants Analyzed: 119   Mean (Standard Deviation)   Unit of Measure: ng/mL  Baseline endoxifen concentration: 119 participants   10.00         (6.00)   4-Month endoxifen concentration: 106 participants   9.30         (5.03)