This study aims to investigate the value of 68Ga-grazytracer in predicting the efficacy of immunotherapy for gastrointestinal malignancies.

The investigators will number all participants, create a medical record file, and record their basic information (gender, age) as well as contact information and medical history information. All participants will undergo a 68Ga-grazytracer PET/CT after 3 cycles of immunotherapy to evaluate response. The imaging response measurements will be compared with the histopathological or clinical assessment results as gold standard.

Inclusion Criteria:

1. Pathological and clinical diagnosis of gastrointestinal malignancies requiring immunotherapy or combination immunotherapy after evaluation according to clinical guidelines.
2. Signed and dated informed consent form.
3. Commitment to comply with research procedures and co-operation in the implementation of the full research process.
4. The patient is in good general condition with an expected survival of > 6 months.
5. aged 18-75 years old.

Exclusion Criteria:

1. Patients with serious illnesses that researchers consider unsuitable for participation in this clinical study. Such as severe heart and lung failure, severe bone marrow suppression, severe liver and kidney dysfunction, etc.
2. Intestinal perforation, complete intestinal obstruction.
3. Pregnant women and women who may be pregnant, women who are breastfeeding.
4. Non-compliant person.

Inpatients and outpatients at Ruijin Hospital who meet the inclusion criteria.