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Z-Endoxifen

Phase 2

Breast Density | Small molecule | Oncology |Atossa Therapeutics, Inc.|Last Updated: May 20, 2026

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLEDDMC
Total Trials1
Total Enrollment240

FDA Designations

ORPHAN_DRUGRARE_PEDIATRIC_DISEASE

Clinical trial landscape

Z-Endoxifen · 1 trial · 1 indication

Phase 2 1
NCT05068388Effect of Oral (Z)-Endoxifen in Premenopausal Women With Measurable Breast DensityBreast Density
COMPLETED240 Analytics
PHASE2COMPLETED
Effect of Oral (Z)-Endoxifen in Premenopausal Women With Measurable Breast Density
Breast DensityUnlock trial analytics

Study Endpoints

Primary Endpoints

Change of mammographic density area (cm2) assessed by iCAD® software
6 months

Change from baseline

Secondary Endpoints

Change of mammographic density area (cm2) assessed by iCAD® software
3 months
Change of mammographic density area (cm2) assessed by Stratus software
6 months
Change from baseline responses to the Breast Cancer Prevention Trial Eight Symptom Scale (BESS)
6 months
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Study Design & Arms

AllocationRANDOMIZED
MaskingQUADRUPLE
ModelPARALLEL
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
PlaceboPLACEBO_COMPARATORoral capsule
1 mg (Z)-endoxifenEXPERIMENTALoral capsule
2 mg (Z)-endoxifenEXPERIMENTALoral capsule

Interventions

NameTypeDescription
Z-EndoxifenDRUGZ-Endoxifen
PlaceboDRUGPlacebo
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Eligibility Criteria

Age Range40 Years to 55 Years
SexFEMALE
Healthy VolunteersYes
Study Sites1

Inclusion Criteria: 1. Premenopausal women (defined as having at least one menstruation during the prior 12 months; women with an intrauterine device are considered premenopausal if \<52 years) 2. Women of childbearing potential using a highly effective method of birth control\* throughout the stud...

Countries:Sweden
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Recent Changes (Last 90 Days)

MEDIUMJun 20, 2026NCT05068388TRIAL_REMOVED: changed
MEDIUMJun 20, 2026NCT05068388TRIAL_REMOVED: changed
MEDIUMJun 20, 2026NCT05068388TRIAL_REMOVED: changed

Frequently asked questions about Z-Endoxifen

What is Z-Endoxifen used for?

Z-Endoxifen is an investigational small molecule being studied for breast density reduction in premenopausal women. It is being developed by Atossa Therapeutics, Inc. (NASDAQ: ATOS) and is currently in Phase 2 clinical development. The drug has received FDA orphan drug designation and rare pediatric disease designation.

What does Z-Endoxifen target?

Z-Endoxifen is an active metabolite of tamoxifen, a selective estrogen receptor modulator. It works by binding to estrogen receptors, thereby modulating estrogen signaling pathways. This mechanism is relevant to its potential effect on breast density, as estrogen influences breast tissue composition.

Who makes Z-Endoxifen?

Z-Endoxifen is being developed by Atossa Therapeutics, Inc., a biopharmaceutical company traded on NASDAQ under the ticker symbol ATOS. The company is conducting clinical trials to evaluate the drug's safety and efficacy for reducing breast density in premenopausal women.

What phase is Z-Endoxifen in?

Z-Endoxifen is in Phase 2 clinical development. It is an investigational drug, meaning it has not been approved by regulatory authorities. A Phase 2 clinical trial has been completed, and the drug is not yet available for commercial use.

What clinical trials is Z-Endoxifen in?

Z-Endoxifen has been studied in a Phase 2 clinical trial with the identifier NCT05068388. This trial, titled 'Effect of Oral (Z)-Endoxifen in Premenopausal Women With Measurable Breast Density,' was a randomized, double-blind, placebo-controlled study conducted in Sweden. It enrolled 240 female participants aged 40 years and older.

Is Z-Endoxifen the same as endoxifen?

Z-Endoxifen is the Z-isomer of endoxifen, which is the active metabolite of tamoxifen. While endoxifen exists as both E and Z isomers, Z-Endoxifen specifically refers to the Z-isomer form being developed by Atossa Therapeutics. This distinction is important for its pharmacological properties and clinical development.