for people ages 18 years and up (full criteria)
at San Francisco, California and other locations
study started
completion around



The purpose of this clinical trial is to learn about the safety and effects of the study medicine (called ARV-471) when given together with other medicines for the potential treatment of advanced or metastatic breast cancer.

This study is seeking participants who have breast cancer that:

  • is advanced, may have spread to other organs (metastatic) and cannot be fully treated by surgery or radiation therapy
  • is sensitive to hormonal therapy (it is called estrogen receptor positive); and
  • is no longer responding to previous treatments This study is divided into separate sub-studies.

For Sub-Study A:

All participants will receive ARV-471 and a medicine called abemaciclib. ARV-471 will be given by mouth, at home, 1 time a day. Abemaciclib will be given by mouth, at home, 2 times a day. We will examine the experiences of people receiving the study medicines. This will help us determine if the study medicines are safe and effective.

Participants will continue to take ARV-471 and abemaciclib until their cancer is no longer responding, or side effects become too severe. They will have visits at the study clinic about every 4 weeks.

Official Title

TACTIVE-U: An Interventional Safety and Efficacy Phase 1b/2, Open-label Umbrella Study to Investigate Tolerability, pk, and Antitumor Activity of Vepdegestrant (ARV-471/PF-07850327), an Oral Proteolysis Targeting Chimera, in Combination With Other Anticancer Treatments in Participants Aged 18 Years and Over With ER+ Advanced or Metastatic Breast Cancer, Sub-study A (ARV-471 in Combination With Abemaciclib)


C4891006 is a sub-study from the Umbrella platform, TACTIVE-U, comprising multiple sub-studies that independently evaluate ARV-471 in participants with Estrogen Receptor Positive (ER+) Advanced or Metastatic Breast Cancer (A/MBC). ARV-471 will act as the backbone therapy given in combination with other anticancer agents thought to have clinical relevance in ER+ breast cancer.


Breast Cancer, TACTIVE-U, Umbrella study, PROTAC, metastatic breast cancer, Breast Neoplasms, ARV-471, Abemaciclib


You can join if…

Open to people ages 18 years and up

  • histological or cytological diagnosis of ER+ and HER2- advanced/metastatic breast cancer that is not amendable to surgical resection with curative intent (≥1% ER+ stained cells on the most recent tumor biopsy).
  • prior anticancer therapies: at least 1 and no more than 2 lines of prior therapies for advanced/metastatic disease; 1 line of any CDK4/6 inhibitor-based regimen is required (independent of the setting eg, adjuvant or advanced/metastatic)
  • at least 1 measurable lesion as defined by RECIST v1.1.
  • ECOG PS ≤1.

You CAN'T join if...

  • visceral crisis at risk of life-threatening complications in the short term
  • known history of drug-induced pneumonitis or other significant symptomatic deterioration of lung functions.
  • newly diagnosed brain metastases, or symptomatic CNS metastases, carcinomatous meningitis, or leptomeningeal disease. Participants with a history of CNS metastases or cord compression are eligible if they have been definitively treated, clinically stable and discontinued anti-seizure medications and corticosteroids for at least 14 days prior to enrollment in the study.
  • history of any other tumor malignancies within the past 3 years, except for the following: (1) adequately treated basal or squamous cell carcinoma of the skin; (2) curatively treated in situ carcinoma of the cervix.
  • inflammatory breast cancer
  • impaired cardiovascular function or clinically significant cardiovascular diseases
  • concurrent administration of medications, food, or herb supplements that are strong inhibitors and strong/moderate inducers of CYP3A and drugs known to predispose to Torsade de Pointes or QT interval prolongation.
  • renal impairment, not adequate liver function and/or bone marrow function
  • known active infection


  • UCSF Medical Center at Mission Bay accepting new patients
    San Francisco California 94158 United States
  • Stanford Women's Cancer Center not yet accepting patients
    Palo Alto California 94304 United States
  • Stanford Women's Cancer Center accepting new patients
    Palo Alto California 94304 United States


accepting new patients
Start Date
Completion Date
To obtain contact information for a study center near you, click here.
Phase 1/2 Breast Cancer Research Study
Study Type
Expecting 40 study participants
Last Updated