Prostatic Neoplasms, Castration-ResistantNCT05968599

A Study to Learn About the Study Medicines Called Enzalutamide and Abiraterone in People With Metastatic Castration-resistant Prostate Cancer

An observational study of Prostatic Neoplasms, Castration-Resistant, run by Pfizer at 1 site in United States.

Completed

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

Trial summary

The purpose of this real-world study is to learn about the effects of 2 study medicines called enzalutamide and abiraterone used to treat metastatic castration-resistant prostate cancer (mCRPC). Prostate cancer is one of the most common cancers in men. The prostate is a gland in the male body that helps make semen. Read more about this study

Who is it for?: Ages 18 years and older, men only
Conditions the study is for: Prostatic Neoplasms, Castration-Resistant
What is being tested?: Enzalutamide and Abiraterone acetate
How many people: 2,731 participants
Where: 1 siteUnited States
Study dates: 24 Jul 2023to 14 Feb 2025
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 18 years and older
Men only
No healthy volunteers
Adult, Older adult

Study population: Men with chemotherapy-naïve mCRPC (aged ≥18 years) who initiated enzalutamide or abiraterone and met eligibility criteria will be included in the study. Patients will be identified from the Flatiron EHR database.

Who may be able to join

Male with metastatic prostate cancer diagnosis and abstracted castration-resistant prostate cancer diagnosis
Initiated enzalutamide or abiraterone within 14 days prior to or after the metastatic castration-resistant prostate cancer diagnosis. The initiation date of enzalutamide or abiraterone will be defined as the index date.
At least 18 years old at the index date

Who cannot join

Received chemotherapy, novel hormonal therapy, radium-223, olaparib/rucaparib, or immunotherapy prior to the index date
Had a prior history of other cancers

Trial locations and contacts

1 site in 1 country.

United States1 site

Pfizer Inc
New York, New York, 10001

Other trials in United States

About this study

Official title: A Real-World Comparison of Clinical Outcomes in Chemotherapy-naive Metastatic Castration-resistant Prostate Cancer (mCRPC) Patients Who Initiated Enzalutamide vs. Abiraterone Acetate (Abiraterone) in Flatiron Electronic Health Record (EHR) Database

The purpose of this real-world study is to learn about the effects of 2 study medicines called enzalutamide and abiraterone used to treat metastatic castration-resistant prostate cancer (mCRPC).

Prostate cancer is one of the most common cancers in men. The prostate is a gland in the male body that helps make semen. Most prostate cancers need male sex hormones, such as testosterone, to grow. Prostate cancer that keeps growing even when the amount of testosterone in the body is reduced to very low levels is known as "castration-resistant". Metastatic cancer is a cancer that has spread to other parts of the body.

This is a real-world study, not a clinical trial. This means that researchers will look at what happens when men receive the treatments prescribed by their own doctor as part of their usual healthcare treatment. In this study, researchers will use information from the Flatiron Electronic Health Record (EHR) database.

The study will include patients' information from the database for men who:

Were confirmed by medical tests to have mCRPC
Started first-line treatment with enzalutamide or abiraterone (index date) for mCRPC
Had not received chemotherapy treatment before index date
Were 18 years of age or older on index date

Men who are part of this study will receive enzalutamide or abiraterone as part of their usual treatment for mCRPC.

We will compare the following between men receiving enzalutamide and men receiving abiraterone:

time from treatment start until death,
treatment duration, and
time to next treatment. This study will use patient information from the database until the end of information that is available.

Conditions: Prostatic Neoplasms, Castration-Resistant
Being tested: Enzalutamide, Abiraterone acetate
Keywords: metastatic castration-resistant prostate cancer, mCRPC, enzalutamide, abiraterone, overall survival, OS, treatment duration
Medical subject headings: Prostatic Neoplasms, Castration-Resistant

What participants receive

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

EnzalutamideDrug
Also called Xtandi
As provided in real-world setting
Abiraterone acetateDrug
Also called Yonsa, Zytiga
As provided in real-world setting

Study groups in NCT05968599
Study group	Role	What they receive
Enzalutamide cohort		Patients with mCRPC initiating enzalutamide Receives: Drug: Enzalutamide
Abiraterone cohort		Patients with mCRPC initiating abiraterone acetate Receives: Drug: Abiraterone acetate

What is being measured

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

Overall Survival (OS): Adjusted Using Inverse Probability Treatment Weighting (IPTW)
OS was defined as the time from the initiation of enzalutamide or abiraterone (i.e., index date) to the date of death. Participants who did not die during this period were censored at their last available follow-up, which was defined as the earlier of end of data availability or last participant contact. Index date was defined as the date of initiation of enzalutamide or abiraterone and their index date was required to occur during the index period. Kaplan-Meier (weighted) method was used for analysis.
Measured: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months

Secondary outcomes (3)

OS Without Subsequent Therapy: Adjusted Using IPTW
OS was defined as the time from the initiation of enzalutamide or abiraterone (i.e., index date) to the date of death. Participants who did not die during this period were censored at their last available follow-up, which was defined as the earlier of end of data availability or last participant contact. Index date was defined as the date of initiation of enzalutamide or abiraterone and their index date was required to occur during the index period. OS of only those participants who initiated abiraterone and enzalutamide on the index date and did not receive subsequent systemic anti-neoplastic therapy were reported in this outcome measure. Kaplan-Meier (weighted) method was used for analysis.
Measured: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months
Time to Treatment Discontinuation (TTD): Adjusted Using IPTW
Treatment duration of the index treatment was defined as the time from the initiation of enzalutamide or abiraterone (i.e., index date) to the discontinuation date. Index date was defined as the date of initiation of enzalutamide or abiraterone and their index date was required to occur during the index period. Discontinuation was defined as the earliest of 1) death, 2) abstracted end date for last enzalutamide or abiraterone drug episode that started within the index treatment line of therapy (LOT) (drug episodes for abstracted oral therapies from the Flatiron Drug Episode table), or 3) day before the start of next LOT. Participants who did not discontinue were censored at their last available follow-up, which was defined as the earlier of end of data availability or last participant contact. Kaplan-Meier (weighted) method was used for analysis.
Measured: From index date to date of treatment discontinuation or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months
Time to Subsequent Therapy (TTST): Adjusted Using IPTW
TTST was defined as the time from the initiation of enzalutamide or abiraterone (i.e., index date) to the start of next LOT. Index date was defined as the date of initiation of enzalutamide or abiraterone and their index date was required to occur during the index period. Participants who did not start a new LOT were censored at their last available follow-up, which was defined as the earliest of 1) death, 2) end of data availability or 3) last participant contact. Kaplan-Meier (weighted) method was used for analysis.
Measured: From index date to date of start of next LOT or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months

Timeline

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

24 Jul 202314 Feb 2025

First posted1 Aug 2023
Study start24 Jul 2023
Primary completion14 Feb 2025
Study completion14 Feb 2025

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 (1)Papers the sponsor has linked to this study.
Other trials for Prostatic Neoplasms, Castration-ResistantStudies 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: 2,731 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05968599
Sponsor's protocol ID: C3431047
Other IDs: NCT05968599
Status last verified: Feb 2026
First submitted: 21 Jul 2023
Last updated: 25 Feb 2026
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: 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

George DJ, Ivanova JI, Touya M, Thompson B, Assayag J, Li B, Kountouris N, Siu G, Freedland SJ. Real-World Overall Survival With Abiraterone Acetate and Enzalutamide in Patients With Chemotherapy-Naive Metastatic Castration-Resistant Prostate Cancer From the Flatiron Electronic Health Records Database. Cancer Med. 2026 Oct;15(10):e72356. doi: 10.1002/cam4.72356.
PubMed 42864777

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

RecruitingPhase 1
Pilot Study for Detection of PSMA-Low CRPC-NE Tumors With Fluciclovine PET/CT
Advanced Prostate Cancer, Metastatic Prostate Cancer
RecruitingPhase 1
Study of JANX007 in Subjects With Metastatic Castration-Resistant Prostate Cancer (ENGAGER-PSMA-01)
Prostate Cancer, Metastatic Castration-resistant Prostate Cancer
RecruitingPhase 1/2
Study of GVV858 as a Single Agent or in Combination With Endocrine Therapy in Patients With HR+/HER2- Breast Cancer and Other Advanced Solid Tumors
Advanced HR+/HER2- Breast Cancer, Advanced CCNE1-amplified Solid Tumors
RecruitingPhase 1/2
A Phase I/II Study of PDS01ADC With Docetaxel and Abiraterone in Adults With Metastatic Castration Sensitive and PDS01ADC With Docetaxel in Castration Resistant Prostate Cancer
Cancer Of Prostate, Prostate Neoplasms
RecruitingPhase 1/2
Docetaxel and SX-682 in Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma, Salivary Gland Carcinoma, and Advanced Prostate Cancer
Head and Neck Cancer, Head and Neck Squamous Cell Carcinoma

All Prostatic Neoplasms, Castration-Resistant trials

Study at a glance

From the registry record, last updated by the sponsor on 25 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Real-World Comparison of Clinical Outcomes in Chemotherapy-naive Metastatic Castration-resistant Prostate Cancer (mCRPC) Patients Who Initiated Enzalutamide vs. Abiraterone Acetate (Abiraterone) in Flatiron Electronic Health Record (EHR) Database
ClinicalTrials.gov ID: NCT05968599
Acronym / sponsor ID: C3431047
Conditions: Prostatic Neoplasms, Castration-Resistant
Keywords: metastatic castration-resistant prostate cancer, mCRPC, enzalutamide, abiraterone, overall survival, OS, treatment duration
Study type: Observational
Recruitment status: Completed
Enrolment: 2,731 participants (actual)
Lead sponsor: PfizerIndustry (pharma, biotech, devices)
Collaborators: Astellas Pharma Inc
Study start: 24 Jul 2023 (actual)
Primary completion: 14 Feb 2025 (actual)
Study completion: 14 Feb 2025 (actual)
First posted: 1 Aug 2023 (actual)
Results: Posted 25 Feb 2026

Clinical summary

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

The purpose of this real-world study is to learn about the effects of 2 study medicines called enzalutamide and abiraterone used to treat metastatic castration-resistant prostate cancer (mCRPC).

The study will include patients' information from the database for men who:

Were confirmed by medical tests to have mCRPC
Started first-line treatment with enzalutamide or abiraterone (index date) for mCRPC
Had not received chemotherapy treatment before index date
Were 18 years of age or older on index date

Men who are part of this study will receive enzalutamide or abiraterone as part of their usual treatment for mCRPC.

We will compare the following between men receiving enzalutamide and men receiving abiraterone:

time from treatment start until death,
treatment duration, and
time to next treatment. This study will use patient information from the database until the end of information that is available.

Study design

Observational model: Cohort
Time perspective: Retrospective
Number of arms: 2

Arm	Type	Receives
Enzalutamide cohort	–	Drug: EnzalutamidePatients with mCRPC initiating enzalutamide
Abiraterone cohort	–	Drug: Abiraterone acetatePatients with mCRPC initiating abiraterone acetate

Who may qualify

Ages: 18 years and older
Sex: Male only
Healthy volunteers: Not accepted
Age groups: Adult, Older adult
Study population: Men with chemotherapy-naïve mCRPC (aged ≥18 years) who initiated enzalutamide or abiraterone and met eligibility criteria will be included in the study. Patients will be identified from the Flatiron EHR database.

Key inclusion criteria (3 listed)

Male with metastatic prostate cancer diagnosis and abstracted castration-resistant prostate cancer diagnosis
Initiated enzalutamide or abiraterone within 14 days prior to or after the metastatic castration-resistant prostate cancer diagnosis. The initiation date of enzalutamide or abiraterone will be defined as the index date.
At least 18 years old at the index date

Key exclusion criteria (2 listed)

Received chemotherapy, novel hormonal therapy, radium-223, olaparib/rucaparib, or immunotherapy prior to the index date
Had a prior history of other cancers

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
EnzalutamideAlso: XtandiAs provided in real-world setting	Drug	Enzalutamide cohort
Abiraterone acetateAlso: Yonsa, ZytigaAs provided in real-world setting	Drug	Abiraterone cohort

Primary outcome

Overall Survival (OS): Adjusted Using Inverse Probability Treatment Weighting (IPTW)
Time frame: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months
OS was defined as the time from the initiation of enzalutamide or abiraterone (i.e., index date) to the date of death. Participants who did not die during this period were censored at their last available follow-up, which was defined as the earlier of end of data availability or last participant contact. Index date was defined as the date of initiation of enzalutamide or abiraterone and their index date was required to occur during the index period. Kaplan-Meier (weighted) method was used for analysis.

3 secondary outcomes

OS Without Subsequent Therapy: Adjusted Using IPTW
Time frame: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months
Time to Treatment Discontinuation (TTD): Adjusted Using IPTW
Time frame: From index date to date of treatment discontinuation or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months
Time to Subsequent Therapy (TTST): Adjusted Using IPTW
Time frame: From index date to date of start of next LOT or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months

Results and safety

Results posted to the registry on 25 Feb 2026, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
Abiraterone	1,316	1,316
Enzalutamide	1,415	1,415

Primary outcome: Overall Survival (OS): Adjusted Using Inverse Probability Treatment Weighting (IPTW)

Time frame: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months. Median (95% Confidence Interval). Unit: Months

Measure	Abiraterone n = 1382	Enzalutamide n = 1257
Value	24.63 (22.93 to 26.33)	25.77 (24.30 to 27.60)

Abiraterone vs Enzalutamide: Cox Proportional Hazard: 1.126 (95% CI 1.0303 to 1.2307), p =0.0088, Sandwich P-values

Population analysed: Analysis population included all participants included in this study, and were adjusted for baseline confounders (demographics, clinical characteristics, prior treatments, comorbidities) using IPTW method. As numbers were adjusted using IPTW, pseudo set was derived. Hence, numbers reported against "Overall Number of Participants Analyzed" (N) for both the arms differ from the unadjusted (raw) numbers presented in participant flow and baseline characteristics section.

3 secondary outcomes are reported in the full results.

Adverse events

Time frame: All-cause mortality: During Data collection period of approximately 104.7 months; retrospective data retrieved and evaluated during approximately 18.7 months; Adverse events: Not applicable as adverse events were not planned to be assessed during the study. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Abiraterone	0 of 0	0 of 0	1,007 of 1,316
Enzalutamide	0 of 0	0 of 0	1,036 of 1,415

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 25 Feb 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Derived from this study: PubMed 42864777George DJ, Ivanova JI, Touya M, Thompson B, Assayag J, Li B, Kountouris N, Siu G, Freedland SJ. Real-World Overall Survival With Abiraterone Acetate and Enzalutamide in Patients With Chemotherapy-Naive Metastatic Castration-Resistant Prostate Cancer From the Flatiron Electronic Health Records Database. Cancer Med. 2026 Oct;15(10):e72356. doi: 10.1002/cam4.72356.
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.

Related trials for Prostatic Neoplasms, Castration-Resistant

RecruitingPhase 1
Pilot Study for Detection of PSMA-Low CRPC-NE Tumors With Fluciclovine PET/CT
Advanced Prostate Cancer, Metastatic Prostate Cancer
RecruitingPhase 1
Study of JANX007 in Subjects With Metastatic Castration-Resistant Prostate Cancer (ENGAGER-PSMA-01)
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RecruitingPhase 1/2
Study of GVV858 as a Single Agent or in Combination With Endocrine Therapy in Patients With HR+/HER2- Breast Cancer and Other Advanced Solid Tumors
Advanced HR+/HER2- Breast Cancer, Advanced CCNE1-amplified Solid Tumors
RecruitingPhase 1/2
A Phase I/II Study of PDS01ADC With Docetaxel and Abiraterone in Adults With Metastatic Castration Sensitive and PDS01ADC With Docetaxel in Castration Resistant Prostate Cancer
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RecruitingPhase 1/2
Docetaxel and SX-682 in Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma, Salivary Gland Carcinoma, and Advanced Prostate Cancer
Head and Neck Cancer, Head and Neck Squamous Cell Carcinoma

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

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

Questions about this trial

What is this clinical trial studying?

An observational study of Prostatic Neoplasms, Castration-Resistant, run by Pfizer at 1 site in United States.

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 3 inclusion and 2 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 25 Feb 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in United States. 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 25 Feb 2026). 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): Adjusted Using Inverse Probability Treatment Weighting (IPTW) (time frame: From index date to date of death or censoring date, whichever occurred first (approximately 104.7 months); retrospective data retrieved and evaluated during approximately 18.7 months). 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 NCT05968599, which also lists 1 linked publication.

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 25 Feb 2026.