Predicting Tamoxifen Dosing for ER+ Breast Cancer Patients

Predicting an Accurate Tamoxifen Dose: a Feasibility Study in Patients With Hormone Sensitive Breast Cancer

This study is testing a new way to personalize tamoxifen dosing for women with ER+ breast cancer to see if it helps them reach the right drug levels and lowers the chance of their cancer coming back.

Quick facts

• Phase: Phase 4
• Study type: Interventional
• Enrollment: 100 (estimated)
• Ages: 18 Years and up
• Sex: Female
• Sponsor: Erasmus Medical Center (Academic / other)
• Locations: 1 site (Rotterdam, Zuid-Holland)
• Trial ID: NCT05525481 on ClinicalTrials.gov

What this trial studies

This study aims to optimize tamoxifen treatment for women with estrogen receptor positive (ER+) breast cancer by using model-informed precision dosing (MIPD). It focuses on the pharmacokinetics of tamoxifen and its active metabolite endoxifen, particularly how genetic variations in the CYP2D6 enzyme affect drug metabolism. By monitoring drug levels and adjusting dosages accordingly, the study seeks to ensure that patients reach the therapeutic endoxifen concentration of at least 16 nmol/L more effectively. This approach could potentially reduce the risk of breast cancer recurrence associated with inadequate drug levels during the initial treatment phase.

Who should consider this trial

Good fit: Ideal candidates for this study are women aged 18 and older who have been prescribed adjuvant tamoxifen treatment for primary ER+ breast cancer.

Not a fit: Patients who have already started tamoxifen treatment for more than two weeks or those with conditions affecting treatment compliance may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could significantly improve treatment outcomes for patients by ensuring they receive the optimal dose of tamoxifen from the start.

How similar studies have performed: Previous studies have shown that therapeutic drug monitoring can significantly improve the likelihood of reaching effective endoxifen levels, indicating that this approach has been successful in similar contexts.

Eligibility criteria

Inclusion Criteria:

1. Age ≥ 18 years;
2. WHO Performance Status ≤ 1 (see Appendix A);
3. Patients with primary breast cancer, with a prescription for adjuvant tamoxifen treatment;
4. Willing to abstain from strong and moderate CYP3A4 or CYP2D6 inhibitors or inducers, according to: CYTOCHROME P450 DRUG INTERACTION TABLE - Drug Interactions (iu.edu);
5. Able and willing to sign the Informed Consent Form;
6. Able and willing to undergo blood sampling for PK analysis.

Exclusion Criteria:

1. Patients with known alcoholism, drug addiction and/or psychiatric or physiological condition which in the opinion of the investigator would impair treatment compliance;
2. \> 2 weeks of tamoxifen treatment before inclusion;
3. Patients who's endoxifen levels have been used for therapeutic drug monitoring in the past.

Where this trial is running

Rotterdam, Zuid-Holland

• Erasmus MC — Rotterdam, Zuid-Holland, Netherlands (Recruiting)

Study contacts

• Study coordinator: Ruben van Nijnatten

Conditions ER+ Breast Cancer