A Study of PET Scans With the Radioactive Tracer 18F-BMS-986229 in Patients With Esophageal, Stomach, or Gastroesophageal Junction Cancer

Inclusion Criteria:

Participant must have pathologically or cytolofically confirmed (at MSK) esophageal, gastric, or gastroesophageal junction adenocarcinoma or squamous cell carcinoma
immunotherapy-drugs-are-boosting-survival/" >PD-L1-positive expression in >/=1% of the tumor or stromal cells. PD-L1 expression will be reviewed by MSK pathologist, scored and recorded using the combined positive score (CPS) formula (number of PD-L1 positive tumor cells, lymphocytes, and macrophages divided by the number of tumor cells x 100).
Participants must have disease that can be evaluated radiographically. This may be measurable disease or nonmeasurable disease according to RECIST 1.1.
Concurrent therapy is allowed.
Age 18 years or older.
Eastern Cooperative Oncology Group (ECOG) performance status 0-2.
Female subjects of childbearing potential must have a negative urine or serum pregnancy test within 24 hours before receiving the first dose of the study medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required.
Adequate organ function, as defined in Table 1. All screening labs should be performed within 14 days of initiation of treatment.

Hematological Absolute neutrophil count: >/=1,000/mCL Platelets: >/=90,000/mCL Hemoglobin: >/=8 g/dL

Renal Serum creatinine:
Hepatic Serum total bilirubin:
Exclusion Criteria:

Known diagnosis of immunodeficiency or receipt of systemic steroid therapy or any other form of immunosuppressive therapy within 7 days before the first dose of trial treatment
History of active tuberculosis (Bacillus tuberculosis)

Active or documented autoimmune or inflammatory disorder (including inflammatory bowel disease, systemic lupus erythematous, Wegener syndrome [granulomatosis with polyangitis], myasthenia gravis, Graves' disease, rheumatoid arthritis, hypophysitis, uveitis) within the 3 years before the start of treatment. The following are exceptions to this criterion:

Subjects with vitiligo or alopecia
Subjects with hypothyroidism (e.g., following Hashimoto syndrome) who are stable with hormone replacement therapy or with psoriasis not requiring systemic treatment