Trial Outcomes & Findings for Study of Elacestrant in Combination With Onapristone in Patients With Advanced or Metastatic Breast Cancer (NCT NCT05618613)
NCT ID: NCT05618613
Last Updated: 2026-07-21
Results Overview
ORR was defined as the proportion of patients achieving confirmed complete or partial response per RECIST v1.1; Phase 2 was not initiated, and no patients were enrolled.
TERMINATED
PHASE1/PHASE2
4 participants
Assessed every 8 weeks until disease progression, up to approximately 6 months
2026-07-21
Participant Flow
Five patients were screened and four were enrolled into Phase 1b Cohort 1 at three U.S. sites.
Participant milestones
| Measure |
Cohort 1
Elacestrant 200mg QD + Onapristone 40mg BID
|
Cohort 2
Elacestrant 300mg QD + Onapristone 40mg BID
|
Cohort 3
Elacestrant 400mg QD + Onapristone 40mg BID
|
Cohort 4
Elacestrant 400mg QD + Onapristone 40mg BID
|
|---|---|---|---|---|
|
Overall Study
STARTED
|
4
|
0
|
0
|
0
|
|
Overall Study
COMPLETED
|
0
|
0
|
0
|
0
|
|
Overall Study
NOT COMPLETED
|
4
|
0
|
0
|
0
|
Reasons for withdrawal
| Measure |
Cohort 1
Elacestrant 200mg QD + Onapristone 40mg BID
|
Cohort 2
Elacestrant 300mg QD + Onapristone 40mg BID
|
Cohort 3
Elacestrant 400mg QD + Onapristone 40mg BID
|
Cohort 4
Elacestrant 400mg QD + Onapristone 40mg BID
|
|---|---|---|---|---|
|
Overall Study
Lack of Efficacy
|
4
|
0
|
0
|
0
|
Baseline Characteristics
Race and Ethnicity were not collected from any participant.
Baseline characteristics by cohort
| Measure |
Cohort 1
n=4 Participants
Cohort 1
|
|---|---|
|
Age, Categorical
<=18 years
|
4 Participants
n=4 Participants
|
|
Age, Categorical
Between 18 and 65 years
|
0 Participants
n=4 Participants
|
|
Age, Categorical
>=65 years
|
0 Participants
n=4 Participants
|
|
Sex: Female, Male
Female
|
4 Participants
n=4 Participants
|
|
Sex: Female, Male
Male
|
0 Participants
n=4 Participants
|
|
Breast Cancer Subtype
|
4 Participants
n=4 Participants
|
|
Disease Status
|
4 Participants
n=4 Participants
|
|
ECOG Performance Status
|
4 Participants
n=4 Participants • The participants Performance Status was evaluated based on the Eastern Cooperative Oncology Group (ECOG) scale. The investigator assesses the patient based on the following scale: Grade 0-1: Ambulatory and capable of self-care, ranging from no restrictions to restricted strenuous activity. Grade 2: Ambulatory and capable of self-care, but unable to work; up \>50% of waking hours. Only patients who scored 0 or 1 were able to enroll in the study. The specific score per patient was not analyzed.
|
PRIMARY outcome
Timeframe: First 28 days (Cycle 1)DLTs were pre-specified toxicities occurring during Cycle 1 (28 days) and considered at least possibly related to study treatment, based on CTCAE criteria. Assessment of safety and tolerability to determine the recommended Phase 2 dose (RP2D). DLT defined as dose associated with \<33% of patients experiencing DLT (≤1 patient out of 6 DLT-evaluable patients).
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Number of Participants With Dose-Limiting Toxicities (DLTs) During First Cycle
|
1 Participants
|
—
|
PRIMARY outcome
Timeframe: Assessed every 8 weeks until disease progression, up to approximately 6 monthsORR was defined as the proportion of patients achieving confirmed complete or partial response per RECIST v1.1; Phase 2 was not initiated, and no patients were enrolled.
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Objective Response Rate (ORR)
|
0 Participants
|
—
|
SECONDARY outcome
Timeframe: From first dose until 30 days after last dose (up to 183 days)Adverse events were collected from first dose through last safety assessment and graded using NCI CTCAE v5.0. Incidence and severity of AEs was collected.
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Adverse Events (AEs)
|
3 Participants
|
—
|
SECONDARY outcome
Timeframe: 183 daysSerious Adverse events were collected from first dose through last safety assessment and graded using NCI CTCAE v5.0. Incidence and severity of SAEs was collected
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Serious Adverse Events (SAEs)
|
0 Participants
|
—
|
SECONDARY outcome
Timeframe: 15 DaysAUC₀-ₜₐᵤ, Cₘₐₓ, Tₘₐₓ, and Cₜᵣₒᵤ for elacestrant, onapristone, and metabolites. PK samples were obtained from 2 patients at Cycle 1, Day 15 at the following timepoints: predose (hour 0), 1, 2, 3, 6, 8, 12, and 24 hours post-dose. Data was collected as represented below for 2 patients
Outcome measures
| Measure |
Elacestrant / Onapristone
n=2 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
n=2 Participants
Cmax
|
|---|---|---|
|
Evaluate the Maximum Plasma Concentration (Cmax) of Elacestrant as Well as Onapristone and Their Metabolites (Phase 1)
Patient 1
|
2,250 ng/mL
|
70.2 ng/mL
|
|
Evaluate the Maximum Plasma Concentration (Cmax) of Elacestrant as Well as Onapristone and Their Metabolites (Phase 1)
Patient 2
|
1,260 ng/mL
|
42.0 ng/mL
|
SECONDARY outcome
Timeframe: 15 DaysAUC₀-ₜₐᵤ, Cₘₐₓ, Tₘₐₓ, and Cₜᵣₒᵤ for elacestrant, onapristone, and metabolites. PK samples were obtained from 2 patients at Cycle 1, Day 15 at the following timepoints: predose (hour 0), 1, 2, 3, 6, 8, 12, and 24 hours post-dose. Data was collected as represented below for 2 patients
Outcome measures
| Measure |
Elacestrant / Onapristone
n=2 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Evaluate the Time of the Maximum Observed Plasma Concentration (Tmax) of Elacestrant as Well as Onapristone and Their Metabolites (Phase 1).
Patient 1
|
6 hours
|
—
|
|
Evaluate the Time of the Maximum Observed Plasma Concentration (Tmax) of Elacestrant as Well as Onapristone and Their Metabolites (Phase 1).
Patient 2
|
6 hours
|
—
|
SECONDARY outcome
Timeframe: From first documented CR/PR until progression or death, up to 183 daysPopulation: Duration of Response (DoR): Not applicable (no confirmed responses)
Time from first CR/PR until progression or death
Outcome measures
| Measure |
Elacestrant / Onapristone
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Evaluate Duration of Response
|
0 Participants
|
—
|
SECONDARY outcome
Timeframe: 183 daysProportion of subjects achieving a best overall or complete response, or durable stable disease (duration is at least 23 weeks)
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Evaluate Clinical Benefit Rate
Stable Disease (SD)
|
1 Participants
|
—
|
|
Evaluate Clinical Benefit Rate
Progressive Disease
|
3 Participants
|
—
|
SECONDARY outcome
Timeframe: 183 DaysPopulation: The population was an Intent to Treat population
Time from the date of the first dose to the date of the first documentation of disease progression or death, whichever occurs first.
Outcome measures
| Measure |
Elacestrant / Onapristone
n=4 Participants
Elacestrant and Onapristone combination
|
Desmethyl Onapristone (Metabolite) Pharmacokinetics
Cmax
|
|---|---|---|
|
Evaluate Progression-free Survival
|
85 Days
Interval 55.0 to 115.0
|
—
|
Adverse Events
Cohort 1
Serious adverse events
Adverse event data not reported
Other adverse events
| Measure |
Cohort 1
n=4 participants at risk
Elacestrant 200mg QD + Onapristone 40mg BID
|
|---|---|
|
General disorders
Fatigue
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
|
Infections and infestations
Urinary tract infection
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
|
Investigations
Blood cholesterol increased
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
|
Musculoskeletal and connective tissue disorders
Muscle spasms
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
|
Psychiatric disorders
Insomnia
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
|
Skin and subcutaneous tissue disorders
Rash maculo-papular
|
25.0%
1/4 • From first dose until 30 days after last dose (up to 183 days)
|
Additional Information
Results disclosure agreements
- Principal investigator is a sponsor employee
- Publication restrictions are in place