NCT04961632

Dose-determining and Dose-confirmatory Study to Investigate the Optimal Dose of Tamoxifen in Breast Cancer Patients According to Genotype Status of TCF20 rs932376

An Open-label, Single-institution, Dose-determining (Part 1) and Dose-confirmatory (Part II) Study to Investigate the Optimal Dose of Tamoxifen in Breast Cancer Patients Harboring Different TCF20 rs932376 Variant Alleles

• Status: Unknown
• Phase: Phase 1
• Study type: Interventional
• Enrollment: 75 (actual)
• Sponsor: National Cancer Centre, Singapore · Academic / Other
• Sex: All
• Age: 21 Years
• Healthy volunteers: Not accepted

Summary

The investigators hypothesize that the TCF20 rs932376 locus controls endoxifen levels in estrogen receptor (ER)-positive breast cancer patients on tamoxifen therapy and that the requirement of tamoxifen dose to achieve therapeutic levels of endoxifen varies according to the genotype status of the patient's at the TCF20 rs932376 locus. Patients will receive escalating doses of tamoxifen according to their TCF20 rs932376 genotype status. Patients on 20mg tamoxifen daily for 8 weeks or longer will provide blood samples for analysis of tamoxifen and its metabolites. Patients assess with \>30nM endoxifen concentrations will continue with 20mg tamoxifen dose. Patients who have endoxifen concentrations \<30nM will receive dose increments of 10mg every 8 weeks until they achieve endoxifen threshold of \>30nM or reach maximum dose level of 40mg/day.

Conditions

• Breast Cancer

Interventions

Type	Name	Description
DRUG	Tamoxifen	Patients taking 20mg tamoxifen will receive dose increments of 10mg every 8 weeks until endoxin threshold of \>30nM or the maximum dose of 40mg/day is reached. The escalated dose will be taken for 1 year before reverting back to 20mg.
DRUG	Tamoxifen	Patients will take tamoxifen at the ascribed genotype-determined dose as determined in the dose-determination phase.

Timeline

• Start date: 2020-12-23
• Primary completion: 2025-11-01
• Completion: 2025-11-01
• First posted: 2021-07-14
• Last updated: 2024-02-01

Locations

1 site across 1 country: Singapore