For Healthcare Professionals

First-in-Human Study of RGT-419B Alone and With Endocrine Therapy in Subjects With HR-Positive, HER2-Negative Advanced/Metastatic Breast Cancer


About the study

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.

Who can take part

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


Inclusion Criteria:

  1. Male or female >/= 18 years old
  2. ECOG Performance Status 0 to 1
  3. HR+, HER2- tumor by most recent biopsy with measurable disease
  4. Have had no more than 1 prior line of cytotoxic chemotherapy in the ABC setting AND no serious/severe toxicity to a prior CKD4/6i AND no known contraindication to receiving RT-419B AND have had all acute/residual toxic effects of any prior therapy
  5. In the ABC setting, eligible subjects must have failed to respond to or progressed after <3 lines of prior CDK4/6i therapy and unlimited lines of prior HT and have had no more than 1 prior line of chemotherapy. Eligible subjects must have received and progressed on any combination of HTs including any approved AI, SERD, or SERM, and/or any approved CDK4/6i in any order.

(5a) For subjects in Arm B, at least one line of prior therapy must have included a locally approved HT which was well tolerated and which the subject is willing to receive again (5b) Subjects with tumors harboring a PIK3CA mutation will be allowed to enroll, and treatment with a PI3Ki in combination with HT will be allowed as a prior line of therapy. Surgical excision of tumor tissue accompanied by chemotherapy or targeted therapy is also counted as 1 line of prior treatment.


Exclusion Criteria:

  1. Presence of visceral metastases with severe organ dysfunction as evidence by signs and symptoms, laboratory studies, lymphangitic spread and/or rapid progression of disease
  2. Pregnant or planning to become pregnant
  3. Prior irradiation to >25% of the bone marrow and/or inadequate bone marrow function or evidence of clinically significant end-organ damage
  4. Major surgery, chemotherapy, targeted therapy, experimental agents, or radiation within 14 days prior to Cycle 1, Day 1
  5. Active, serious medical condition that is not well controlled with locally approved medications allowed by the protocol
  6. History of allergic reactions attributed to compounds of similar chemical or biologic composition to the drugs used in the study
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


Breast Cancer

Age (in years)



Phase 1

Participants needed


Est. Completion Date

Aug 28, 2024

Treatment type



Regor Pharmaceuticals Inc. 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.