A Phase 3 interventional study of PF-07220060 and letrozole in Breast Cancer, sponsored by Pfizer. Active, not recruiting at 460 sites in 30 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-16.
Sponsored by Pfizer · Phase 3, Interventional, and Treatment
The purpose of this study is to determine the safety and efficacy of PF-07220060 with letrozole compared to approved treatments (ie, palbociclib, ribociclib or abemaciclib with letrozole) in people with breast cancer:
Approximately half of the participants will receive PF-07220060 plus letrozole while the other half of participants will receive the investigator's choice of treatment plus letrozole.
The study team will monitor how each participant is doing with the study treatment during regular visits at the study clinic.
14,825 studies on the registry are indexed under Breast Neoplasms; 3,319 are open to participants now.
This study's enrollment of 1,035 is above the median of 72 across 10,896 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Pfizer is the lead sponsor of 3,334 studies on the registry; 149 are open to participants now.
Of its 601 completed or terminated interventional studies of FDA-regulated products, 391 (65%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
The standard rules for measuring tumours on CT or MRI scans, to tell whether a cancer is shrinking, stable or growing during treatment.
“Measurable disease per RECIST 1.1” usually means at least one tumour 10 mm or more at its longest on a CT scan, or a lymph node 15 mm or more across its short axis.
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Metastases
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HER2
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Measurable disease
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
RECIST
The standard rules for measuring tumours on CT or MRI scans, to tell whether a cancer is shrinking, stable or growing during treatment.
“Measurable disease per RECIST 1.1” usually means at least one tumour 10 mm or more at its longest on a CT scan, or a lymph node 15 mm or more across its short axis.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Adjuvant and neoadjuvant
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
PF-07220060 tablet taken by mouth plus Letrozole tablet taken by mouth
Drug: PF-07220060 · Drug: letrozole
Investigator's Choice of CDK4/6 inhibitor (tablet/capsule) taken by mouth with letrozole tablet taken by mouth
Drug: letrozole · Drug: abemaciclib · Drug: palbociclib · Drug: ribociclib
CDK4 inhibitor
endocrine therapy
CDK4/6 inhibitor
CDK4/6 inhibitor
CDK4/6 inhibitor
Progression Free Survival (PFS) by BICR
Time from the date of randomization to the date of the first documentation of objective progressive disease as determined by blinded independent central review (BICR) per RECIST v1.1, or death due to any cause, whichever occurs first
Time frame: From the date of randomization until disease progression or death due to any cause (up to approximately 4 years)
Overall Survival (OS)
Time from the date of randomization to the date of death due to any cause
Time frame: From the date of randomization until death due to any cause (up to approximately 13 years).
Progression Free Survival (PFS) by Investigator
Time from the date of randomization to the date of the first documentation of objective progressive disease as determined by investigator per RECIST v1.1, or death due to any cause, whichever occurs first
Time frame: From the date of randomization until disease progression or death due to any cause (up to approximately 4 years)
OR by BICR and by investigator
Time from randomization date (every 8 weeks during the first 48 weeks and then every 12 weeks) to the date of progression OR death whichever occurs first
Time frame: From randomization to progression or death whichever occurs first (up to approximately 4 years)
Duration of Response (DoR) by BICR and by investigator
Time from the date of CR or PR to the first documentation of objective progressive disease, or death due to any cause, whichever occurs first
Time frame: From the date of CR or PR until objective progressive disease, or death (up to approximately 4 years)
Incidence of treatment emergent treatment related adverse events (AE)
Incidence and severity of AEs graded according to the NCI CTCAE v5.0
Time frame: Duration of the study approximately up to 13 years.
Incidence of treatment emergent treatment related serious adverse events
Incidence and severity of AEs graded according to NCI CTCAE v5.0
Time frame: Duration of the study approximately up to 13 years.
Estimated mean change from baseline in EORTC QLQ C30
Time frame: Baseline to end of treatment (up to approximately 4 years)
Estimated mean change from baseline in BPI-SF
Time frame: Baseline to end of treatment (up to approximately 4 years)
Estimated mean change from baseline in EQ-5D-5L
Time frame: Baseline to end of treatment (up to approximately 4 years)
Estimated mean change from baseline in EORTC Breast Cancer Module (BR42)
Time frame: Baseline to end of treatment (up to approximately 4 years)
Mean change from baseline of ctDNA
Time frame: Baseline to end of treatment (up to approximately 4 years)
Showing the first 100 of 460 sites across 30 countries. Choose a country and city above to see the rest.
Plan to share: Yes — 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.
Data sharing details ↗ · www.pfizer.com
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is active, not recruiting, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Atirmociclib