The purpose of this study is to learn how much of the study medicine called Vepdegestrant will reach the bloodstream when given orally compared to given intravenously.

This study is seeking participants who:

• are healthy males and healthy females who cannot have children.
• are 18 years or older.
• are healthy as decided by medical tests.
• have a body mass index (BMI) of 16 to 32 kilogram per meter squared.
• have a total body weight of more than 45 kilograms (99 pounds).

In Period 1, all participants will receive one dose of Vepdegestrant by IV. In Period 2, all participants will receive one dose of Vepdegestrant by mouth following a high-fat breakfast. The levels of Vepdegestrant in Period 1 will be compared to the levels of Vepdegestrant in Period 2 and the bioavailablility of the oral formulation of Vepdegestrant will be determined.

The study duration is 22 days and includes two periods. Participants will stay in the clinical research unit for 9 days (8 nights) during each period. A follow-up visit for each participant takes place at 28 to 35 days after taking the study medicine for the last time.

Key Inclusion Criteria:

1. Male participants, and/or female participants of non-childbearing potential who are healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and cardiac monitoring.
2. Body mass index (BMI) of 16-32 kg/m2; and a total body weight >45 kg (99 lb).

Key Exclusion Criteria:

1. Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurological, or allergic disease.

   • Any condition possibly affecting drug absorption (eg, gastrectomy, cholecystectomy)
   • History of or positive testing for HIV infection, hepatitis B, or hepatitis C.

2. Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality or other conditions that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.

3. Use of prescription or nonprescription drugs and dietary and herbal supplements, grapefruit/grapefruit containing products, and Seville orange/Seville orange containing products within 7 days or 5 half lives (whichever is longer) prior to the first dose of study intervention.

4. Previous administration with an investigational product (drug or vaccine) within 30 days or 5 half lives preceding the first dose of study intervention used in this study (whichever is longer).

5. A positive urine drug test

6. Screening blood pressure ≥140/90 mm Hg for participants <60 years; and ≥150/90 mm Hg for participants ≥60 years old.

7. Renal impairment as defined by an eGFR in adults <60 mL/min/1.73 m² based on CKD-EPI equation.

8. Standard 12 lead electrocardiogram that demonstrates clinically relevant abnormalities that may affect participant safety or interpretation of study results (eg, QTcF >450 ms, complete left bundle branch block, signs of a myocardial infarction, ST T interval changes suggestive of myocardial ischemia, second or third degree AV block, or serious bradyarrhythmias or tachyarrhythmias).

9. History of alcohol abuse or repeated binge drinking and/or any other illicit drug use or dependence within 6 months of Screening.

10. 6 months prior or current use of tobacco or nicotine-containing products in excess of the equivalent of 5 cigarettes/day or 2 chews of tobacco/day.

11. History of sensitivity to heparin or heparin-induced thrombocytopenia.

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.