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Advanced Breast CancerPhase 1NCT07897721

A Study to Learn About the Study Medicine Called PF-08165784 in People With PIK3CA-Mutated Advanced or Metastatic Solid Tumors

A Phase 1 study testing PF-08165784, Fulvestrant and Atirmociclib in people with Advanced Breast Cancer and Advanced or Metastatic Breast Cancer, run by Pfizer.

Not yet recruiting

Opening soon. The study is approved but enrolment has not started yet. Sites may already take enquiries.

Sites and contacts
Official record
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Trial summary

The purpose of this study is to learn about the safety and effects of the study medicine (called PF-08165784) when given alone or together with other anti-cancer therapies. Anti-cancer therapy is a type of treatment given to stop the growth of cancer. Read more about this study

Who is it for?
Ages 18 years and older
What is being tested?
PF-08165784, Fulvestrant and Atirmociclib
Type of treatment
Pill or oral medicine
Could I receive a placebo?
No, everyone receives an active treatment
How many people
268 participants
Where
No sites listed yet
Study dates
9 Nov 2026to 21 Mar 2032
Phase
Phase 1
Are there results?
Not yet: the study is under way

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 18 years and older
  • All sexes
  • No healthy volunteers
  • Adult, Older adult

Who may be able to join

  • 18 years of age or older
  • Advanced or metastatic cancer of the breast or colon Part 1A, 1B, and 1C: HR+/HER2- advanced or metastatic breast cancer with disease progression after at least 1 line of treatment with an endocrine therapy and cyclin-dependent kinase (CDK)4/6 inhibitor in the advanced or metastatic setting and received no more than 1 line of prior cytotoxic and/or 1 line of prior antibody-drug conjugate (ADC) therapy in the metastatic setting Part 1D: Metastatic or advanced colorectal cancer with at least having received chemotherapy and/or targeted therapy if appropriate Part 2A: HR+/HER2- advanced or metastatic breast cancer with no prior systemic therapy or chemotherapy for advanced or metastatic disease
  • Phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) mutation
  • Archived tumor specimen or fresh tumor biopsy
  • Measurable disease
  • Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1

Who cannot join

  • Active or clinically significant dermatologic conditions
  • Active malignancy within 3 years prior to enrollment
  • Advanced/metastatic, symptomatic, visceral spread, that are at risk of life-threatening complications in the short term
  • Major surgery or radiation therapy within 3 weeks prior to study entry
  • Prior irradiation to >25% of the bone marrow
  • Active or history of pneumonitis/interstitial lung disease requiring corticosteroids
Show all 15Show fewer
  • Unmanageable ascites
  • Prior treatment with phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway inhibitors may be permitted in certain study cohorts and excluded in others, as specified by the study protocol.
  • Renal impairment
  • Hepatic dysfunction
  • Hematologic abnormalities
  • Uncontrolled diabetes
  • Cardiac abnormalities
  • Active or history of clinically significant gastrointestinal (GI) or inflammatory GI disease
  • Other unacceptable abnormalities or prohibited therapies as defined by protocol

Trial locations and contacts

No sites are listed yet. Contact the study team or a site near you to ask about taking part.

Pfizer CT.gov Call Center contact

1-800-718-1021

ClinicalTrials.gov_Inquiries@pfizer.com

About this study

Official title: A PHASE 1 DOSE ESCALATION AND EXPANSION STUDY TO EVALUATE SAFETY, TOLERABILITY, PHARMACOKINETICS, PHARMACODYNAMICS, AND ANTI-TUMOR ACTIVITY OF PF-08165784 MONOTHERAPY AND COMBINATIONS IN PARTICIPANTS WITH PIK3CA-MUTATED ADVANCED OR METASTATIC SOLID TUMORS

The purpose of this study is to learn about the safety and effects of the study medicine (called PF-08165784) when given alone or together with other anti-cancer therapies. Anti-cancer therapy is a type of treatment given to stop the growth of cancer. This study also aims to find the best amount of study medication that can be given to patients.

This study is seeking participants with a specific type of breast cancer (BC) called hormone receptor-positive (HR+), HER2- negative (HER2-) breast cancer, or colorectal cancer (CRC) (cancer of the colon or rectum), that has a change (mutation) in a gene called PIK3CA. The cancer must be advanced or metastatic, meaning it has spread to other parts of the body or cannot be completely removed with surgery.

All participants in this study will take the study medication (PF-08165784) as a tablet by mouth. The participant may take the medicine at the study clinic during study visits or at home. Treatment will be given in 28-day cycles and will continue for as long as the participant remains in the study. Depending on which part of the study participants are enrolled into, they will receive the study medication (PF-08165784) alone or in combination with other anti-cancer medications.

Being tested
PF-08165784, Fulvestrant, Atirmociclib, Cetuximab, Letrozole
Keywords
Carcinoma, Breast, Estrogen Receptor Positive Breast Cancer, HER2- Breast Cancer, Colon Cancer, PI3K mutation
Medical subject headings
Breast Neoplasms, Carcinoma, Colonic Neoplasms

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • PF-08165784Drug

    Taken by mouth (PO)

  • FulvestrantDrug

    Also called Faslodex

    Selective Estrogen Receptor Degrader (SERD)

  • AtirmociclibDrug

    Also called PF-07220060

    Selective cyclin-dependent kinase 4 (CDK4) inhibitor

  • CetuximabDrug

    Also called Erbitux

    Monoclonal antibody (EGFR inhibitor)

  • LetrozoleDrug

    Also called Femara

    Nonsteroidal aromatase inhibitor

Study groups in NCT07897721
Study groupRoleWhat they receive
Part 1 Dose Escalation Cohort 1AExperimentalPF-08165784 monotherapy dose escalation for participants with advanced or metastatic BC at different doses of the study drug
Receives: Drug: PF-08165784
Part 1 Dose Escalation Cohort 1BExperimentalCombination (PF-08165784 + fulvestrant) dose escalation for participants with advanced or metastatic BC, at different doses of the study drug
Receives: Drug: PF-08165784; Drug: Fulvestrant
Part 1 Dose Escalation Cohort 1CExperimentalCombination (PF-08165784 + fulvestrant + atirmociclib) dose escalation for participants with advanced or metastatic BC, at different doses of the study drug
Receives: Drug: PF-08165784; Drug: Fulvestrant; Drug: Atirmociclib
Part 1 Dose Escalation Cohort 1DExperimentalCombination (PF-08165784 + cetuximab) dose escalation for participants with advanced or metastatic CRC at different doses of the study drug
Receives: Drug: PF-08165784; Drug: Cetuximab
Part 2 Dose Optimization/Expansion Cohort 2AExperimentalCombination (PF-08165784 + letrozole + atirmociclib) dose optimization/expansion for participants with advanced or metastatic BC, at different doses of the study drug
Receives: Drug: PF-08165784; Drug: Atirmociclib; Drug: Letrozole

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Part 1 (Dose Escalation): Number of participants with Dose-Limiting Toxicities (DLT)

    Any adverse events that are attributable to one, the other, or both study treatments, occurring in the DLT observation period are considered DLTs, excluding toxicities clearly due to underlying disease or extraneous causes.

    Measured: Baseline up to 28 days

  2. Part 1 (Dose Escalation): Incidence of Adverse Events (AEs)

    An adverse event (AE) was any untoward medical occurrence in a participant who received study medication without regard to possibility of causal relationship to it.

    Measured: From start of treatment up to 30 days after last dose or start of new anticancer therapy, whichever occurred first

  3. Part 1 (Dose Escalation): Number of participants with laboratory abnormalities

    Number of participants with laboratory test abnormalities.

    Measured: From start of treatment up to 30 days after last dose or start of new anticancer therapy, whichever occurred first

  4. Part 2 (Dose Expansion): Objective Response Rate (ORR)

    ORR defined as per Response Evaluation Criteria in Solid Tumors (RECIST v1.1).

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

Secondary outcomes (16)

  1. Part 1: Objective Response Rate (ORR) as per Response Evaluation Criteria in Solid Tumors (RECIST v1.1)

    ORR is defined as the percentage of participants in the analysis population having a best overall response (BOR) of confirmed complete response (CR) or confirmed partial response (PR) according to RECIST v1.1.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  2. Part 1 & Part 2: Disease Control Rate (DCR) as per RECIST v1.1

    DCR is defined as the proportion of participants with CR or PR with confirmation, or Stable Disease (SD) per RECIST version 1.1.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  3. Part 1 & Part 2: Clinical Benefit Rate (CBR) as per RECIST v1.1

    CBR is defined as the percentage of participants with a best overall response of CR or PR at any time before Progressive Disease (PD), or non-CR/non-PD or SD for at least 24 weeks from start date of treatment and prior to PD, relative to the appropriate analysis set.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  4. Part 1 & Part 2: Duration of Response (DOR) as per RECIST v1.1

    DOR is defined as the time from first documentation of CR or PR to date of first documentation of PD or death due to any cause.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  5. Part 1 & Part 2: Progression-Free Survival (PFS) as per RECIST v1.1

    PFS is defined as time from start date of treatment to the date of first documentation of PD or death due to any cause.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  6. Part 1 & Part 2: Time to Response (TTR) as per RECIST v1.1

    TTR is defined as the time from start date of treatment to first documentation of CR or PR.

    Measured: Baseline and every 8 to 12 weeks through time of confirmed disease progression, death, unacceptable toxicity, or through study completion (approximately 2 years)

  7. Part 1: Maximum Observed Serum Concentration (Cmax) & Trough Concentration (Ctrough)

    Evaluate the single and multiple dose pharmacokinetic (s) (PK) of PF-08165784 as monotherapy, or in combination with other anti-tumor agents.

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  8. Part 1: Time to Reach Maximum Observed Serum Concentration (Tmax)

    Evaluate the single and multiple dose PK of PF-08165784 as monotherapy, or in combination with other anti-tumor agents.

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  9. Part 1: Area Under the Curve (AUC) from Time Zero to Last Quantifiable Concentration (AUClast)

    Evaluate the single and multiple dose PK of PF-08165784 as monotherapy, or in combination with other anti-tumor agents.

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  10. Part 1: Effect of Food on Cmax

    Evaluate the effect of food on Cmax of PF-08165784 as monotherapy

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  11. Part 1: Effect of Food on Tmax

    Evaluate the effect of food on Tmax of PF-08165784 as monotherapy

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  12. Part 1: Effect of Food on AUClast

    Evaluate the effect of food on AUClast of PF-08165784 as monotherapy

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  13. Part 2 (Dose Expansion): Number of participants with laboratory abnormalities

    Number of participants with laboratory test abnormalities.

    Measured: From start of treatment up to 30 days after last dose or start of new anticancer therapy, whichever occurred first

  14. Part 2 (Dose Expansion): Incidence of Adverse Events (AEs)

    An adverse event (AE) was any untoward medical occurrence in a participant who received study medication without regard to possibility of causal relationship to it.

    Measured: From start of treatment up to 30 days after last dose or start of new anticancer therapy, whichever occurred first

  15. Part 2 (Dose Expansion): Pre- and post-dose concentrations of PF-08165784

    Evaluate the pre- and post-dose concentrations of PF-08165784

    Measured: Baseline through end of Cycle 1 (each cycle is 28 days)

  16. Part 2: Overall Survival (OS)

    OS is defined as time from from start date of treatment to the date of death due to any cause

    Measured: Up to approximately 2 years

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted27 Oct 2026
  2. Study start9 Nov 2026 (estimated)
  3. Primary completion22 Mar 2030 (estimated)
  4. Study completion21 Mar 2032 (estimated)

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 1
Primary purpose
Treatment
Allocation
Non-randomised
Intervention model
Sequential
Masking
None (open label)
Enrolment
268 participants (estimated)
IDs, dates and publications
ClinicalTrials.gov ID
NCT07897721
Sponsor's protocol ID
C6631001
Status last verified
Oct 2026
First submitted
20 Oct 2026
Last updated
27 Oct 2026
Results posted
No
Data monitoring committee
No
FDA-regulated drug
Yes
FDA-regulated device
No
Individual data sharing
No: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Questions about this trial

What is this clinical trial studying?

A Phase 1 study testing PF-08165784, Fulvestrant and Atirmociclib in people with Advanced Breast Cancer and Advanced or Metastatic Breast Cancer, run by Pfizer.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 6 inclusion and 15 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: opening soon, as of the sponsor's last update on 27 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

This study is still under way. Results are not available in the source record yet.

How can a doctor refer a patient or contact the research team?

Contact Pfizer CT.gov Call Center (1-800-718-1021, ClinicalTrials.gov_Inquiries@pfizer.com), or a site near the patient. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Part 1 (Dose Escalation): Number of participants with Dose-Limiting Toxicities (DLT) (time frame: Baseline up to 28 days). The study lists 4 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT07897721.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 27 Oct 2026; AzTrials last refreshed its copy on 28 Oct 2026.

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