Breast CancerNCT04735367

Study to Evaluate Overall Survival in Japanese Patients With HR+/HER2- Advanced Breast Cancer Treated With Palbociclib Plus Letrozole

An observational study of Breast Cancer, run by Pfizer at 13 sites in Japan.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record

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Trial summary

Who is it for?: Ages 20 years and older, women only
Conditions the study is for: Breast Cancer
What is being tested?: palbociclib plus letrozole
How many people: 42 participants
Where: 13 sitesJapan
Study dates: 3 Feb 2021to 29 Sep 2023
Phase: Observational
Are there results?: Yes, posted in the registrySummary in the doctors' view

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 20 years and older
Women only
No healthy volunteers
Adult, Older adult

Study population: Patients who participated, treated with palbociclib plus letrozole, and under follow-up for survival in J-Ph2

Who may be able to join

Participated, treated with palbociclib plus letrozole in J-Ph2, and was under follow-up for survival at the study completion of J-Ph2.
For patients who are still alive and have routine visits to the study site, evidence of a personally signed and dated informed consent document indicating that the patient has been informed of all pertinent aspects of the study. For patients who are still alive and had been transferred to another hospital, evidence that the patient has been informed of all pertinent aspects of the study and oral or written informed consent is obtained. For patients who had already passed away, the conduct of this study will be disclosed, and the patients' legally acceptable representatives will be guaranteed an opportunity to refuse data collection for the patients in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects

Who cannot join

1. There are no exclusion criteria for this study.

Trial locations and contacts

13 sites in 1 country.

City, postcode or hospital

13 sites in 1 country

Japan13 sites

Chiba cancer center
Chiba, Chiba, 260-8717
National Cancer Center Hospital
Chuo-ku, Tokyo, 104-0045
National Hospital Organization Kyushu Cancer Center
Fukuoka, 811-1395
Hiroshima City Hiroshima Citizens Hospital
Hiroshima, Hiroshima, 730-8518
Hakuaikai Medical Corporation Sagara Hospital
Kagoshima, 892-0833
Saitama Cancer Center
Kita-adachi-gun, Saitama, 362-0806
Kumamoto University Hospital
Kumamoto, Kumamoto, 860-8556
Kumamoto Shinto General Hospital
Kumamoto, 862-8655
Kyoto University Hospital
Kyoto, 606-8507
National Hospital Organization Shikoku Cancer Center
Matsuyama, Ehime, 791-0280
Aichi Cancer Center
Nagoya, 464-8681
National Hospital Organization - Osaka National Hospital - Institute For Clinical Research
Osaka, 540-0006
National Hospital Organization Hokkaido Cancer Center
Sapporo, Hokkaido, 003-0804

Other trials in Japan

About this study

Official title: Retrospective, Multicenter, Observational Study to Evaluate Overall Survival in Japanese Patients With HR+/HER2- Advanced Breast Cancer Treated With Palbociclib Plus Letrozole

This is a retrospective, multicenter, observational study in Japan. The primary objective is to evaluate overall survival (OS) in Japanese patients with HR+/HER2- advanced breast cancer who have been treated with palbociclib plus letrozole. This observational study was planned as follow-up study of Japanese phase 2 study of palbociclib (NCT01684215, phase 2 portion of A5481010 study).

Conditions: Breast Cancer
Being tested: palbociclib plus letrozole
Keywords: retrospective, multicenter, observational study, Japan, HR+/HER2- advanced breast cancer, palbociclib, overall survival
Medical subject headings: Breast Neoplasms

What participants receive

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

palbociclib plus letrozoleDrug
palbociclib plus letrozole

What is being measured

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

Overall Survival (OS)
OS was defined as the time from the date of the first dose of the investigational product in Japanese Phase 2 study (A5481010) to the date of any-cause death. In the absence of confirmation of death, survival time was censored to last date the participant was known to be alive. Kaplan-Meier method was used for analysis.
Measured: From the date of the first dose of the treatment in study A5481010 to the date of any-cause death or censoring date (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study

Secondary outcomes (2)

Percentage of Participants According to Types and Line of Subsequent Treatment
Participants were classified based on types of subsequent treatment and by line of subsequent treatment. Subsequent treatments included: endocrine therapy-based, chemotherapy-based and others (Investigational drug + Endocrine therapy/Chemotherapy).
Measured: From start of subsequent treatment in study A5481010 until date of death, withdrawal of consent or end of study (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study
Duration of Subsequent Therapy by Line of Therapy
Duration of subsequent therapy defined as time from the start date to the end date of each line of treatment among participants who received subsequent treatment. Kaplan-Meier method was used.
Measured: From start of subsequent treatment in study A5481010 until date of death, withdrawal of consent or end of study (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study

Timeline

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

3 Feb 202129 Sep 2023

First posted3 Feb 2021
Study start3 Feb 2021
Primary completion29 Sep 2023
Study completion29 Sep 2023

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Publications (2)Papers the sponsor has linked to this study.
Other trials for Breast CancerStudies of the same condition, open and under way.
More trials run by PfizerThe sponsor's other registered studies.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

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

Study design

Study type: Observational
Observational model: Cohort
Time perspective: Retrospective
Enrolment: 42 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT04735367
Sponsor's protocol ID: A5481154
Other IDs: NCT04735367
Status last verified: Nov 2025
First submitted: 28 Jan 2021
Last updated: 9 Dec 2025
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: No
FDA-regulated drug: No
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.

Publications

Takahashi M, Yasojima H, Osako T, Inoue K, Kawashima M, Maeda H, Ito M, Sagara Y, Yonemori K, Hattori M, Yamamoto N, Muramatsu Y, Matsui A, Masuda N. Overall survival and subsequent therapy patterns in Japanese patients with ER+/HER2- advanced breast cancer treated with palbociclib plus letrozole in the first-line setting: a final analysis. Breast Cancer. 2025 Nov;32(6):1482-1490. doi: 10.1007/s12282-025-01760-0. Epub 2025 Aug 21.
PubMed 40841781
Takahashi M, Osako T, Yasojima H, Inoue K, Kawashima M, Maeda H, Ichikawa A, Muramatsu Y, Masuda N. Overall survival in Japanese patients with ER+/HER2- advanced breast cancer treated with first-line palbociclib plus letrozole. Breast Cancer. 2024 Jan;31(1):53-62. doi: 10.1007/s12282-023-01511-z. Epub 2023 Oct 26.
PubMed 37882974

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

See locations

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All Breast Cancer trials

Study at a glance

From the registry record, last updated by the sponsor on 9 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: Retrospective, Multicenter, Observational Study to Evaluate Overall Survival in Japanese Patients With HR+/HER2- Advanced Breast Cancer Treated With Palbociclib Plus Letrozole
ClinicalTrials.gov ID: NCT04735367
Acronym / sponsor ID: A5481154
Conditions: Breast Cancer
Keywords: retrospective, multicenter, observational study, Japan, HR+/HER2- advanced breast cancer, palbociclib, overall survival
Study type: Observational
Recruitment status: Completed
Enrolment: 42 participants (actual)
Lead sponsor: PfizerIndustry (pharma, biotech, devices)
Study start: 3 Feb 2021 (actual)
Primary completion: 29 Sep 2023 (actual)
Study completion: 29 Sep 2023 (actual)
First posted: 3 Feb 2021 (actual)
Results: Posted 9 Dec 2025

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Study design

Observational model: Cohort
Time perspective: Retrospective

Who may qualify

Ages: 20 years and older
Sex: Female only
Healthy volunteers: Not accepted
Age groups: Adult, Older adult
Study population: Patients who participated, treated with palbociclib plus letrozole, and under follow-up for survival in J-Ph2

Key inclusion criteria (2 listed)

Participated, treated with palbociclib plus letrozole in J-Ph2, and was under follow-up for survival at the study completion of J-Ph2.
For patients who are still alive and have routine visits to the study site, evidence of a personally signed and dated informed consent document indicating that the patient has been informed of all pertinent aspects of the study. For patients who are still alive and had been transferred to another hospital, evidence that the patient has been informed of all pertinent aspects of the study and oral or written informed consent is obtained. For patients who had already passed away, the conduct of this study will be disclosed, and the patients' legally acceptable representatives will be guaranteed an opportunity to refuse data collection for the patients in accordance with the Ethical Guidelines for Medical and Health Research Involving Human Subjects

Key exclusion criteria (1 listed)

1. There are no exclusion criteria for this study.

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
palbociclib plus letrozolepalbociclib plus letrozole	Drug	–

Primary outcome

Overall Survival (OS)
Time frame: From the date of the first dose of the treatment in study A5481010 to the date of any-cause death or censoring date (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study
OS was defined as the time from the date of the first dose of the investigational product in Japanese Phase 2 study (A5481010) to the date of any-cause death. In the absence of confirmation of death, survival time was censored to last date the participant was known to be alive. Kaplan-Meier method was used for analysis.

2 secondary outcomes

Percentage of Participants According to Types and Line of Subsequent Treatment
Time frame: From start of subsequent treatment in study A5481010 until date of death, withdrawal of consent or end of study (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study
Duration of Subsequent Therapy by Line of Therapy
Time frame: From start of subsequent treatment in study A5481010 until date of death, withdrawal of consent or end of study (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study

Results and safety

Results posted to the registry on 9 Dec 2025, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
Palbociclib+ Letrozole	42	42

Primary outcome: Overall Survival (OS)

Time frame: From the date of the first dose of the treatment in study A5481010 to the date of any-cause death or censoring date (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study. Median (95% Confidence Interval). Unit: Months

Measure	Palbociclib+ Letrozole n = 42
Value	85.42 (64.26 to NA)

Population analysed: Analysis set included participants who were enrolled in J-Ph2 and received the investigational product excluding surviving participants who did not give written or oral consent.

2 secondary outcomes are reported in the full results.

Adverse events

Time frame: For all-cause mortality: From start of subsequent treatment in study A5481010 until date of death, withdrawal of consent or end of study (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in study A5481154. Data for non-serious adverse events and serious adverse events (SAEs) were not collected and evaluated during the study; hence timeframe is not applicable for non-SAEs and SAEs.. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Palbociclib+ Letrozole	0 of 0	0 of 0	20 of 42

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 9 Dec 2025.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Derived from this study: PubMed 40841781Takahashi M, Yasojima H, Osako T, Inoue K, Kawashima M, Maeda H, Ito M, Sagara Y, Yonemori K, Hattori M, Yamamoto N, Muramatsu Y, Matsui A, Masuda N. Overall survival and subsequent therapy patterns in Japanese patients with ER+/HER2- advanced breast cancer treated with palbociclib plus letrozole in the first-line setting: a final analysis. Breast Cancer. 2025 Nov;32(6):1482-1490. doi: 10.1007/s12282-025-01760-0. Epub 2025 Aug 21.
Derived from this study: PubMed 37882974Takahashi M, Osako T, Yasojima H, Inoue K, Kawashima M, Maeda H, Ichikawa A, Muramatsu Y, Masuda N. Overall survival in Japanese patients with ER+/HER2- advanced breast cancer treated with first-line palbociclib plus letrozole. Breast Cancer. 2024 Jan;31(1):53-62. doi: 10.1007/s12282-023-01511-z. Epub 2023 Oct 26.
To obtain contact information for a study center near you, click here.Link provided by the sponsor.
Individual participant dataSharing planned: 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.

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Not yet recruitingObservational study
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RecruitingPhase 3
Testing Whether Hormone Therapy With Ribociclib is as Effective as Chemotherapy Followed by Hormone Therapy With Ribociclib for the Treatment of High Anatomic Stage Breast Cancer With Low Recurrence Risk, The RxFINE-Low Trial
Anatomic Stage II Breast Cancer AJCC v8, Anatomic Stage IIIA Breast Cancer AJCC v8

Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Pfizer CT.gov Call Center study director

Pfizer

13 sites in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

An observational study of Breast Cancer, run by Pfizer at 13 sites in Japan.

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 2 inclusion and 1 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: finished, as of the sponsor's last update on 9 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 13 sites in Japan. Whether a site is taking part right now should be confirmed with that site. See every site.

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.

Are results available for this study?

Yes. Results are posted in the registry (first posted 9 Dec 2025). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

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

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Overall Survival (OS) (time frame: From the date of the first dose of the treatment in study A5481010 to the date of any-cause death or censoring date (maximum of 103.16 months of follow-up); data collected and observed retrospectively over 32 months in A5481154 study). 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 NCT04735367, which also lists 2 linked publications.

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 9 Dec 2025.