A Phase 1 interventional study of RGT-419B and RGT-419B in combination with hormonal therapy in Breast Cancer, sponsored by Regor Pharmaceuticals Inc.. Recruiting at 8 sites in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-08-12.
Sponsored by Regor Pharmaceuticals Inc. · Phase 1, Interventional, and Treatment
This is a phase I, First-in-Human (FIH), open-label study to evaluate the safety, tolerability, pharmacokinetic (PK) profile, and preliminary efficacy of RGT-419B administered orally as monotherapy OR in combination with Hormonal Therapy in subjects with HR+, HER2- locally advanced and unresectable (Stage III) or metastatic (Stage IV) breast cancer whose disease has progressed during prior therapy with an approved CDK4/6i plus hormonal therapy.
12,544 studies on the registry are indexed under Breast Neoplasms; 2,892 are open to participants now.
This study's planned enrollment of 64 is below the median of 72 across 9,303 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Regor Pharmaceuticals Inc. is the lead sponsor of 7 studies on the registry; 2 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Eligible subjects must meet all of the following criteria:
Progression after receiving 1 line of prior cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) therapy combined with HT in the MBC setting (up to 1 additional line of CDK4/6i is permitted in the post-surgical adjuvant setting);
Progression after ≤3 lines of prior HT therapy (regardless of whether it is HT alone or in combination with other therapies)
Exclusion Criteria:
RGT-419B given alone as monotherapy
Drug: RGT-419B
RGT-419B in combination with Hormonal Therapy
Drug: RGT-419B in combination with hormonal therapy
oral capsules
RGT-419B in combination with hormonal therapy (Selective Estrogen Receptor Degrader, Selective Estrogen Receptor Modulator, or Aromatase Inhibitor)
Safety & Tolerability - Number of subjects with Dose-Limiting Toxicities (DLTs) at each cohort dose level in singlet and doublet therapy
Number of subjects who have a confirmed DLT at each cohort dose level in singlet and doublet study arms during the first 28-day cycle of RGT-419B treatment.
Time frame: 4 weeks (1 cycle)
Safety & Tolerability - Incidence, Severity, and Causality of all Treatment Emergent Adverse Events (TEAEs)
Incidence, severity, and causality of all TEAEs will be assessed for all patient participating from Day 1 dosing through end of study.
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Cmax
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Area Under Concentration-Time Curve (AUC0-t)
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Area Under Concentration-Time Curve to Infinity (AUC0-inf)
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Plasma Decay Half-Life (t 1/2)
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Time to Reach Maximum Observed Plasma Concentration (Tmax)
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Accumulation rate after multiple doses
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Day 1 and steady-state PK assessment of RGT-419B and major metabolites - Cumulative urinary excretion
Plasma and urine samples that are being collected for PK assessment may also be used for exploratory metabolite identification
Time frame: through study completion, an average of 1 year
Tumor Response assessed by Investigator according to RECIST v1.1
Tumor response measured by radiologic imaging techniques at baseline and throughout the study
Time frame: through study completion, an average of 1 year
QTc Interval - Changes in corrected QT interval
Number of subjects with a clinically significant increase from baseline in corrected QT (QTc) interval on repeated ECGs during RGT-419B monotherapy.
Time frame: through study completion, an average of 1 year
Symptom Burden
Change from baseline in symptom burden on the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-C30 (EORTC QLQ-C30) from baseline to end of treatment
Time frame: through study completion, an average of 1 year
Eligibility is decided by the study team. Share this record with your doctor or contact the team directly.
Contact study teamGet an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Regor Pharmaceuticals Inc.