This study is to evaluate the safety, biodistribution, radiation dosimetry and tumor uptake of the [68Ga]/ [131I]-IR199 in patients with Claudin 18.2 positive gastric cancer and pancreatic cancer.

Inclusion Criteria:

1. Informed consent must be obtained in writing from the subject, their legally authorized representative, or caregiver.
2. Age equal to or above 18 years old.
3. Histologically or cytologically confirmed gastric cancer or pancreatic cancer with Claudin 18.2 expression.
4. Must have ≥1 Claudin 18.2 positive lesions.

Exclusion Criteria:

1. Less than two weeks since the last treatment that could cause bone marrow suppression.
2. Known or suspected history of ≥3 grade renal and urinary system diseases.
3. Medical history of allergy, hypersensitivity reaction or intolerance to radioactive drugs.