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-endoxifen

Phase 2

Breast Neoplasms | Small molecule | Oncology |Atossa Therapeutics, Inc.|Last Updated: Oct 30, 2025

Success Probability
Approval Probability 71%
TA Base Rate26%
Adjusted LOA41%
ML RiskLOW_RISK
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Market & Valuation
rNPV $3.2B
Market Size $9.4B
Revenue Basis $1.6B
Competitors 6
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Trial Design
CONTROLLEDDMCBiomarker
Total Trials1
Total Enrollment87
FDA Designations
ORPHAN_DRUGRARE_PEDIATRIC_DISEASE
Clinical Trials (1)
NCT IDTitlePhaseStatusEnrollmentVelocityDesignStartCompletionLast UpdatedSitesCountries
NCT05607004(Z)-Endoxifen for the Treatment of Premenopausal Women With ER+/HER2- Breast CancerPHASE2 RECRUITING 87Feb 14, 2023Apr 1, 2027Oct 30, 202515 United States
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Study Endpoints
Primary Endpoints
PK Cohort - (Z)-endoxifen steady-state plasma concentrations
After 4 weeks of treatment

(Z)-endoxifen steady-state plasma concentrations (Css) of evaluable subjects who completed at least one cycle of treatment (28 +/- 3 days)

For Analysis of Cohort A (Treatment Cohort): determine whether the week 4 Ki-67≤10% rate is at least 65%
After 4 weeks of treatment

For analysis Cohort A (subjects that have a baseline Ki-67\>10%): the primary objective is to determine whether the Week 4 Ki-67 ≤ 10% rate is at least 65% among premenopausal women with primary estrogen receptor positive (ER+), Human Epidermal Growth Factor Receptor 2 negative (HER2-) breast cancer.

For analysis Cohort B (Treatment Cohort): determine the objective tumor response rate at 24 weeks
After 24 weeks of treatment

For analysis Cohort B (subjects have baseline Ki-67≤ 10%): the primary objective is to determine the objective tumor response rate at 24 weeks among premenopausal women with ER+, HER2-, Ki-67 ≤ 10% breast cancer receiving (Z) endoxifen plus goserelin.

Secondary Endpoints
PK Cohort - Area under the plasma (Z)-endoxifen concentration-time curve from time zero to last measurable concentration
Days 1 and 28
PK Cohort - Area under the plasma (E)-endoxifen concentration-time curve from time zero to last measurable concentration
Days 1 and 28
PK Cohort - Accumulation and accumulation half-life
Days 1 and 28
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Study Design & Arms
AllocationNON_RANDOMIZED
MaskingNONE
ModelPARALLEL
PurposeTREATMENT
Treatment Arms
ArmTypeDescription
PK CohortEXPERIMENTAL(Z)-endoxifen capsules orally once daily for 4 weeks. Initial (Z)-endoxifen dose evaluated will be 40 mg with an option to evaluate 20 mg or 80 mg. The PK Cohort participants may extend treatment based on Ki-67% at Week 4. If Ki-67 ≤ 10% at Week 4, participant will be offered option to continue on this treatment for up to 6 cycles/Week 24. Each cycle is 28 days. If Ki-67 \> 10% at Week 4, participant will be withdrawn and go on to surgery.
Treatment Cohort - Single Treatment ArmEXPERIMENTAL(Z)-endoxifen 40mg capsules orally once daily for 4 weeks + goserelin 3.6 mg by subcutaneous implant approximately every 28 days. (Z)-endoxifen 40mg dose based on results of PK Cohort. If Ki-67 ≤ 10% at Week 4, continue on this treatment for up to 6 cycles/Week 24. Each cycle is 28 days. And then go on to surgery within 3 weeks of Cycle 6 day 26. If Ki-67 \> 10% at Week 4, participant will complete early termination assessments.
PK Cohort 80 mgEXPERIMENTAL(Z)-endoxifen 80 mg capsules orally once daily for 4 weeks. The PK Cohort participants may extend treatment based on Ki-67% at Week 4. If Ki-67 ≤ 10% at Week 4, participant will be offered option to continue on this treatment for up to 6 cycles/Week 24. Each cycle is 28 days. If Ki-67 \> 10% at Week 4, participant will be withdrawn and go on to surgery.
PK Cohort 80 mg + OFSEXPERIMENTAL(Z)-endoxifen 80 mg capsules orally once daily for 4 weeks + goserelin 3.6 mg by subcutaneous implant approximately every 28 days. The PK Cohort participants may extend treatment based on Ki-67% at Week 4. If Ki-67 ≤ 10% at Week 4, participant will be offered option to continue on this treatment for up to 6 cycles/Week 24. Each cycle is 28 days. If Ki-67 \> 10% at Week 4, participant will be withdrawn and go on to surgery.
Interventions
NameTypeDescription
(Z)-endoxifenDRUG(Z)-endoxifen capsules. Doses of (Z)-endoxifen to be evaluated include 20 mg (two x 10 mg capsules), 40 mg (one 40 mg capsule) and 80 mg (two x 40 mg capsules).
goserelinDRUGgoserelin 3.6 mg subcutaneous implant
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Eligibility Criteria
Age Range18 Years — N/A
SexFEMALE
Healthy VolunteersNo
Study Sites15

Inclusion Criteria: 1. Female sex assigned at birth. Female to male transgender individuals who have not had any hormonal therapy may be considered for the trial after review and approval from the medical monitor and study sponsor. 2. Age 18 years or older 3. Not lactating, pregnant, or planning to...

Countries:United States
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Recent Changes (Last 90 Days)
LOWMay 26, 2026NCT05607004primaryCompletionDate: changed
LOWMay 24, 2026NCT05607004studyFirstPostDate: changed