Genotype and Phenotype Guided Supplementation of TAMoxifen Standard Therapy With ENDOXifen in Breast Cancer Patients

  • End date
    Dec 26, 2021
  • participants needed
  • sponsor
    Robert Bosch Gesellschaft für Medizinische Forschung mbH
Updated on 26 January 2021
body mass index
tubal ligation
hormonal contraception
breast cancer
neutrophil count
tumor cells
carcinoma in situ
cancer treatment
ductal carcinoma in situ
breast cancer staging
ductal carcinoma


In hormone-receptor positive breast cancer or DCIS (ductal carcinoma in situ) tamoxifen remains an important treatment option for patients before menopause and those patients after menopause who cannot be treated with aromatase-inhibitors. Nonetheless, a considerable amount of patients suffer a relapse of their cancer while on treatment with tamoxifen. Tamoxifen is a drug that is metabolized to a variety of compounds by the human liver, and the most important antihormonally active metabolite is called (Z)-Endoxifen. It is known that patients who have a reduced or absent activity of the drug-metabolizing enzyme CYP2D6 have lower levels of (Z)-Endoxifen. Furthermore, it has been observed that patients on tamoxifen therapy who have absent CYP2D6 activity are at a 2-fold increased risk for disease recurrence, and patients with lower CYP2D6 compared to patients with normal CYP2D6 activity still have a 1.4-fold increased risk for disease recurrence.

This trial will include patients who are already on tamoxifen therapy for at least 3 months and is designed to show that in patients with absent or low CYP2D6 activity, (Z)-Endoxifen supplementation - that is giving (Z)-Endoxifen in addition to tamoxifen for the study period of 42 days - can increase blood levels of (Z)-Endoxifen to therapeutic concentrations. It is planned to included 504 patients in this blinded, randomized trial, which will have a placebo group (receiving no (Z)-Endoxifen) and two intervention groups that will receive 0, 1.5 or 3 mg (Z)-Endoxifen depending on their CYP2D6 genetics or their (Z)-Endoxifen levels at the start of the study.

The trial is not designed to evaluate outcome measures (that is recurrence or survival rates) of (Z)-Endoxifen supplementation in tamoxifen treated patients, but will document the safety of the combined administration of tamoxifen and (Z)-Endoxifen.

Condition Ductal Carcinoma In Situ, Adenocarcinoma, Breast Cancer, Breast Cancer Diagnosis, Ductal Carcinoma In Situ (DCIS), Malignant Adenoma, breast carcinoma, cancer, breast, dcis
Treatment (Z)-Endoxifen supplementation according to genotype, (Z)-Endoxifen supplementation according to plasma levels
Clinical Study IdentifierNCT03931928
SponsorRobert Bosch Gesellschaft für Medizinische Forschung mbH
Last Modified on26 January 2021


Yes No Not Sure

Inclusion Criteria

Written informed consent obtained prior to study entry. The patient must be accessible for scheduled visits and treatment
Pre- and postmenopausal women with ductal carcinoma in situ (DCIS) or early stage breast cancer. This includes stage I, IIA, IIB, and IIIA breast cancers
ER+/PR+, ER+/PR- or ER-/PR+ receptor status. Criteria for endocrine sensitivity is 1% ER-positive or PR-positive tumor cells on immune-histochemical staining
Patients on standard tamoxifen monotherapy (20 mg/d) for at least three months or patients who had switched from AI to tamoxifen who are on tamoxifen treatment for at least three months
Age 18 years
Body mass index of 18.5 to 35.0 kg/m2
The Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1
Absolute neutrophil count greater than or equal to 1 500/L
Platelets greater than or equal to 100 000/L
Total bilirubin within less than or equal to 1.5 times institutional upper limit of normal
AST/ALT less than or equal to 2.5 times institutional upper limit of normal
The subjects need to be either
of non-childbearing potential (documented postmenopausal status, defined as no menses for 12 months without an alternative medical cause, or post hysterectomy, bilateral salpingectomy or bilateral oophorectomy) or
of childbearing potential (WOCBP) with negative serum pregnancy test (due to the known reproduction toxicity of tamoxifen found in preclinical studies, WOCBP need to use a highly effective non-hormonal contraception. These are copper IUDs, bilateral tubal ligation, a vasectomized partner (vasectomy at least three months prior to screening) or sexual abstinence. Male or female condoms with/ without spermicide or caps, diaphragms or sponges with spermicide are associated with a failure rate > 1% per year and are thus not sufficient during the intervention period
Resolution of all acute toxic effects of prior anti-cancer therapy or surgical procedures to NCI CTCAE version 5.0 Grade 2 (except alopecia or other toxicities not considered a safety risk for the patient at investigator's discretion)
Surgery and radiation therapy of the breast has to be completed upon study entry

Exclusion Criteria

Subjects who are unable to understand written and verbal instructions
Locally advanced (Stadium IIIB or IIIC) or metastatic (Stage IV) breast cancer at the time of surgery
Ongoing chemotherapy and/or treatment with trastuzumab within the last three months; participation in another trial with any investigational/not-marketed drug within 3 months prior to baseline visit
Other active second malignancy
Invalid result of genotyping
Breast feeding/lactation
Oral contraceptives containing estrogens and/or progesterones
Pathologic vaginal bleeding in pre-menopausal women or vaginal bleeding in post-menopausal patients
Current severe acute somatic or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or may interfere with the interpretation of study results and, in judgement of the investigator, would make the patient inappropriate for entry into this study
Severe chronic cardiac or pulmonary disease (heart failure NYHA class 3 and 4), COPD GOLD C or D
Chronic or acute renal disease with a glomerular filtration rate < 60 ml/min/1.73 m2, and any patient on peritoneal dialysis or hemodialysis
Medical history of thromboembolism (deep vein thrombosis or pulmonary embolism)
QTc interval >0.47 sec at screening ECG
Concurrent treatment with strong to moderate inhibitors of CYP2D6 which may alter tamoxifen metabolism (Consortium on Breast Cancer Pharmacogenomics 2008)
paroxetine, fluoxetine, bupropion, quinidine and duloxetine, diphenhydramine
thioridazine, amiodarone, cimetidine, sertraline
\. Known allergies against an ingredient of the investigational product or
Clear my responses

How to participate?

Step 1 Connect with a site
What happens next?
  • You can expect the study team to contact you via email or phone in the next few days.
  • Sign up as volunteer to help accelerate the development of new treatments and to get notified about similar trials.

You are contacting

Investigator Avatar

Primary Contact


Preferred Language
Other Language
Please verify that you are not a bot.

Additional screening procedures may be conducted by the study team before you can be confirmed eligible to participate.

Learn more

If you are confirmed eligible after full screening, you will be required to understand and sign the informed consent if you decide to enroll in the study. Once enrolled you may be asked to make scheduled visits over a period of time.

Learn more

Complete your scheduled study participation activities and then you are done. You may receive summary of study results if provided by the sponsor.

Learn more

Similar trials to consider


Browse trials for

Not finding what you're looking for?

Every year hundreds of thousands of volunteers step forward to participate in research. Sign up as a volunteer and receive email notifications when clinical trials are posted in the medical category of interest to you.

Sign up as volunteer

user name

Added by • 



Reply by • Private

Lorem ipsum dolor sit amet consectetur, adipisicing elit. Ipsa vel nobis alias. Quae eveniet velit voluptate quo doloribus maxime et dicta in sequi, corporis quod. Ea, dolor eius? Dolore, vel!

  The passcode will expire in None.

No annotations made yet

Add a private note
  • abc Select a piece of text from the left.
  • Add notes visible only to you.
  • Send it to people through a passcode protected link.
Add a private note