For Healthcare Professionals

Endoxifen in Adults With Hormone Receptor Positive Solid Tumors


About the study

Background: Some types of cancer cells that have hormone receptors on their surfaces need the hormone estrogen to grow. The drug tamoxifen blocks estrogen from binding to the tumor cells, which helps to slow or stop the growth of cancer. Tamoxifen has been approved for treatment of certain types of estrogen-linked cancers, such as breast and ovarian cancer. The experimental drug Z-Endoxifen HCl (endoxifen) is related to tamoxifen, and has been shown to work against similar estrogen-linked cancers. In many cancer patients, tamoxifen is turned into endoxifen by enzymes in the liver; however, not all people have the liver enzymes that can turn tamoxifen into endoxifen, which means that the drug cannot work properly. Taking certain other drugs at the same time as tamoxifen can also keep it from turning into endoxifen. Researchers are interested in determining whether endoxifen tablets are effective in slowing or stopping tumor growth in individuals whose hormone-linked tumors have not responded to standard treatment. Objectives: - To test the safety and effectiveness of daily endoxifen in individuals with hormone receptor positive solid tumors that have not responded to standard treatment. Eligibility: - Individuals at least 18 years of age who have been diagnosed with hormone receptor positive solid tumors (breast or other tumors), desmoid tumors, or gynecologic tumors that have not responded to standard treatment. Individuals with breast cancer must have had at least one prior chemotherapy regimen and one prior hormonal regimen for metastatic disease. Design: Participants will be screened with a full medical history (including prior hormone use) and physical examination, as well as blood and urine tests, tumor imaging studies, and an eye examination. Participants will take endoxifen tablets daily for 28-day cycles of treatment, and will be asked to keep a medication diary to record any side effects. Participants will have regular clinic visits with blood and urine samples and imaging studies to evaluate the cancer's response to treatment. Participants will continue to take endoxifen for as long as the cancer responds to the treatment.

Who can take part

You may be eligible to participate in the study if you meet the following criteria:



Patients with the following types of histologically documented solid tumors:

  1. ER +/PR+, ER+/PR-, or ER-/PR+ breast cancer
  2. Gynecologic tumors (endometrial, ovarian, uterine, fallopian tube, peritoneal, etc.)
  3. Desmoid tumors
  4. Tumors that are ER+ or PR+ by immunohistochemistry (including low-level expression) such as non-small cell lung, colorectal, and prostate

Patients with breast cancer must have had at least one prior chemotherapy regimen for metastatic disease. Additionally, patients with breast cancer must have received prior tamoxifen and/or aromatase inhibitor therapy (if postmenopausal) with at least one hormonal regimen in the metastatic setting. Patients with HER2+ breast cancer must have progressed after at least one prior HER2-directed regimen (trastuzumab, lapatinib) for metastatic disease.

All other patients must have disease that has progressed following at least one line of standard therapy. Prior therapy with tamoxifen is allowed.

Patients enrolled based on tumor ER/PR status must have ER/PR status confirmed by the Laboratory of Pathology, NIH. ER/PR status will be determined on a metastatic site, if possible; otherwise, the original site or available tissue will be acceptable.

Patients must have recovered to at least eligibility levels following any display of adverse events and/or toxicity due to prior chemotherapy or biologic therapy. They must not have had hormonal therapy, chemotherapy or biologic therapy within 4 weeks prior to entering the study (6 weeks for nitrosoureas or mitomycin C, or UCN-01). Patients must be greater than or equal 2 weeks since any prior administration of study drug in a Phase 0 study (also referred to as an "early Phase I study" or "pre-Phase I study" where a sub-therapeutic dose of drug is administered) at the PI's discretion. Patients must be greater than or equal to 4 weeks since any prior radiation or major surgery. However, patients receiving bisphosphonates or therapeutic anticoagulation are eligible for this trial.

Age greater than or equal 18 years

The Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to 2

Life expectancy > 3 months

Patients must have normal or adequate organ and marrow function as defined below:

Absolute neutrophil count greater than or equal to 1,500/microL

Platelets greater than or equal to 100,000/microL

Total bilirubin within less than or equal to 1.5 times institutional upper limit of normal

AST (SGOT)/ALT (SGPT) less than or equal to 2.5 times institutional upper limit of normal

Creatinine < 1.5 times upper limit of normal


Creatinine clearance greater than or equal to 60 mL/min/1.73 m(2) for patients with creatinine levels greater than or equal to 1.5 times upper limit of normal.

The effects of Z-endoxifen on the developing human fetus are unknown. For this reason, women of childbearing potential and men must agree to use adequate nonhormonal contraception (barrier method of birth control or abstinence) prior to study entry, for the duration of study participation, and for 2 months after discontinuation from the study. Women of childbearing potential must have a negative pregnancy test in order to be eligible. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with Z-endoxifen, breastfeeding should be discontinued if the mother is treated with Z-endoxifen.

Ability to understand and the willingness to sign a written informed consent document.



Patients receiving any other investigational agents.

Patients with known brain metastases are excluded from this clinical trial, with the exception of patients whose brain metastatic disease status has remained stable for greater than or equal to 3 months after treatment of the brain metastases, without steroids or anti-seizure medications. These patients may be enrolled at the discretion of the principal investigator.

Patients with clinically significant illnesses which could compromise participation in the study, including, but not limited to, uncontrolled infection, uncontrolled diabetes, uncontrolled hypertension, symptomatic congestive heart failure, unstable angina pectoris, myocardial infarction within the past 6 months, uncontrolled cardiac arrhythmia, stroke/cerebrovascular accident within the past 6 months, or psychiatric illness/social situations that in the investigator s opinion would make it undesirable for the patient to participate in the trial, or which would jeopardize compliance with the protocol.

Patients with untreated spinal cord metastases or metastases close to vital organs (as determined by the principal investigator) are excluded because of the risk of hormonal flare.

Patients with a history of deep vein thrombosis must be on anti-coagulation therapy prior to enrollment. Patients requiring prophylactic anti-coagulation are eligible.

pin location

Study Locations

Enter your ZIP code/Postal code/PIN code to locate study sites near you:

How to Apply

Contact the study center to learn if this study is a good match for you.

Study’s details


Hormone Receptor-Positive Breast,Gynecologic,Desmoid,Hormone Receptor-Positive Neoplasms

Age (in years)



Phase 1

Participants needed


Est. Completion Date

Jun 1, 2024

Treatment type



National Institutes of Health Clinical Center (CC) identifier


Study number


Understanding Clinical Trials

Get answers to your questions about clinical trials.What is a clinical research?What does taking part in clinical trials involve?What should I ask the trial doctor?


Sign up to save your favorites, 
receive newsletters, resources, and alerts 
about clinical trials related to your conditions of interest.