Symbiotic-GI-16: A Study to Learn About the Study Medicine Called PF-08634404 in Combination With Chemotherapy in Gastroesophageal Cancer

Phase 2: Confirmed Objective response rate (ORR) using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

Confirmed ORR by investigator is defined as the proportion of participants with confirmed Complete Response (CR) or Partial Response (PR) per RECIST v1.1 as assessed by investigator.

Phase 2: Number of participants with treatment-emergent adverse events

Timeframe: Through 90 days after the last study intervention; Approximately 4 years

Adverse Events (AEs) as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), timing, seriousness, and relationship to study intervention.

Phase 3: Progression Free Survival (PFS) using RECIST 1.1 as assessed by BICR

Timeframe: Approximately 4 years

PFS by BICR is defined as the time from the date of randomization to the date of first documented disease progression per RECIST 1.1 as assessed by BICR, or death due to any cause, whichever occurs first.

Phase 3: Overall Survival (OS)

Timeframe: Approximately 4 years

OS is defined as the time from the date of randomization to the date of death due to any cause.

Phase 2: Duration of Response (DOR) using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

DOR by investigator is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, respectively, or death due to any cause, whichever occurs first.

Phase 2: Progression Free Survival (PFS) using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

PFS by investigator is defined as the time from the date of first dose to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, or death due to any cause, whichever occurs first.

Phase 2: Overall Survival (OS)

Timeframe: Approximately 4 years

OS is defined as the time from the date of first dose to the date of death due to any cause.

Phase 2: Number of participants with laboratory abnormalities

Timeframe: Through 90 days after the last study intervention; Approximately 4 years

Laboratory abnormalities as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), and timing. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, high, low, or not done and be listed.

Phase 2: Serum concentrations of PF-08634404

Timeframe: Approximately 21 months

Predose and postdose concentrations of PF-08634404

Phase 2: Incidence of Anti-Drug Antibody (ADA) against PF-08634404

Timeframe: Approximately 21 months

Phase 3: ORR using RECIST 1.1 as assessed by BICR

Timeframe: Approximately 4 years

ORR by BICR is defined as the proportion of participants with a Best Overall Response (BOR) of confirmed CR or confirmed PR per RECIST 1.1 as assessed by BICR.

Phase 3: ORR using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

ORR by investigator is defined as the proportion of participants with a BOR of confirmed CR or confirmed PR per RECIST 1.1 as assessed by investigator.

Phase 3: Progression free survival (PFS) using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

PFS by investigator is defined as the time from the date of randomization to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, or death due to any cause, whichever occurs first

Phase 3: DOR using RECIST 1.1 as assessed by BICR

Timeframe: Approximately 4 years

DOR is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by BICR, respectively, or death due to any cause, whichever occurs first.

Phase 3: DOR using RECIST 1.1 as assessed by investigator

Timeframe: Approximately 4 years

DOR is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, respectively, or death due to any cause, whichever occurs first.

Phase 3: PFS2 (PFS after next-line therapy) by investigator

Timeframe: Approximately 4 years

PFS2 is defined as the time from the date of randomization to the date of second objective disease progression or death due to any cause, whichever occurs first

Phase 3: Number of participants with treatment-emergent adverse events

Timeframe: Through 90 days after the last study intervention; Approximately 4 years

AEs as characterized by type, frequency, intensity as graded by NCI CTCAE version 5.0, timing, seriousness, and relationship to study intervention(s)

Phase 3: Number of participants with laboratory abnormalities

Timeframe: Through 90 days after the last study intervention; Approximately 4 years

Laboratory abnormalities as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), and timing. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, high, low, or not done and be listed.

Phase 3: Serum concentrations of PF-08634404

Timeframe: Approximately 21 months

Predose and postdose concentrations of PF-08634404

Phase 3: Incidence of ADA against PF-08634404

Timeframe: Approximately 21 months

Phase 3: Change from baseline in Functional Assessment of Cancer Therapy - Gastric (FACT-Ga) Total score

Timeframe: Approximately 4 years

Phase 3: Time to definitive deterioration in FACT-Ga Total score

Timeframe: Approximately 4 years

Phase 3: Time to definitive deterioration in Gastric Cancer Subscale (GaCS) score

Timeframe: Approximately 4 years