A Study of a Medicine Called Atirmociclib in Combination With Giredestrant in Adult Participants With ER-positive, HER2-negative Early-stage Breast Cancer

What this study involves

The registry does not currently label this study as recruiting. Ask about its status before planning a screening visit.

Study type

Interventional

Phase

Phase 3

Age range

18 years - Not specified

Sex eligible

All sexes

Healthy volunteers

Not accepted

Participants

3800 Estimated

These are starting points, not an eligibility decision. The research team must review the full requirements.

About the research

This Phase 3 study will evaluate whether atirmociclib plus giredestrant improves invasive breast cancer-free survival compared with giredestrant alone in adults with ER-positive, HER2-negative early breast cancer at medium or high risk of recurrence.

This is a Phase 3, double blind, placebo controlled study of atirmociclib plus giredestrant vs. giredestrant monotherapy as adjuvant treatment in adult patients with ER+, HER2- early breast cancer. The study plans to enroll 3800 participants randomized 1:1 into one of two treatment arms (Arm A - investigational: atirmociclib plus giredestrant taken continuously in a 28-day cycle) or (Arm B - comparator: placebo plus giredestrant taken continuously in a 28-day cycle). Participants may be treated with atirmociclib/placebo up to 3 years and giredestrant up to 5 years followed by long term follow up for survival and evaluation of recurrence of disease.

Who may be able to participate?

The list below is the sponsor’s full registry wording. It can include conditions, prior treatment, test results and other requirements. A match in search does not mean you qualify.

KEY INCLUSION CRITERIA

1. Histologically confirmed unilateral primary adenocarcinoma of the breast

* ER-positive by local assessment
* documented HER2-negative
2. Node positive or node negative as defined by:

• Pathological node positive (microscopic and/or macroscopic tumor involvement \>/=pN1)
• pN0 and pT \>1cm with at least one of the following:

1. pT4N0 or
2. histologically Grade 3 disease or
3. high-risk classification based on genomic assay
3. Randomization within 16 months of definitive breast surgery
4. If indicated, completed adjuvant and/or neoadjuvant chemotherapy, adjuvant radiation therapy \>/= 21 days prior to randomization

KEY EXCLUSION CRITERIA

1. Distant metastases of breast cancer beyond regional lymph nodes
2. Multicentric or multifocal breast cancer if any tumor foci meet pathologic criteria for ER(-) or HER2(+)
3. Clinically significant cardiovascular disease or cardiac repolarization abnormality for 6 months prior to randomization; resting heart rate \<50bpm
4. Has received the following prior systemic anti-cancer therapy for breast cancer

• prior atirmociclib, giredestrant, other investigational anti-cancer agent
• prior treatment with olaparib

NOTES:
* short course of prior neo/adjuvant CDK4/6 inhibitor treatment (\</=8 weeks) is permitted; 10-day washout period required
* short course of prior neoadjuvant and/or adjuvant ET (\</=18 weeks) is permitted; 35-day washout period for tamoxifen is required
5. Prior treatment with investigational product within 30 days or 5 half-lives

Treatment, groups and participation

The registry may describe treatments and study duration without a complete visit calendar. Ask the study team for the exact schedule, procedures, risks, costs and alternatives. Keep your usual care plan unless your treating clinician tells you otherwise.

Assignment

Random assignment

Masking

Quadruple masked

What researchers are measuring

Outcome measures describe what is being studied. They are not proof that a treatment works.

Primary measures

Secondary measures

Research locations (0)

The overall study status and a local site’s status can differ. Confirm that location’s availability before traveling.

No locations are listed. Use the official study contact.

Study team and timeline

Lead sponsor

Pfizer

Study start

Dec 1, 2026 Estimated

Primary completion

Apr 13, 2032 Estimated

Study completion

Aug 20, 2042 Estimated

First posted

Oct 22, 2026 Actual

Last updated

Nov 10, 2026 Actual

Official study contacts