To evaluate the potential usefulness of 18F-AlF-FAPi-04 PET/CT for the diagnosis of primary and metastatic lesions in solid cancer.

This is a prospective, single-center, two arms, open label, non-randomized study to evaluate the ability of 18F-AlF-FAPi-04 to detect FAP expressing cells in patients with solid tumor, evaluate its biological distribution characteristics, impact on clinical treatment plans, and evaluate imaging differences between different probes. Taking histopathology and imaging follow-up as gold standard, the sensitivity, specificity, and accuracy of 18F-AlF-FAPi-04 PET/CT will be calculated.

Inclusion Criteria:

1. Obtain/sign informed consent.

2. Age ≥18 years, male or female patients.

3. Histologically or cytologically confirmed digestive tumors, head and neck squamous cell carcinoma, or peritoneal metastases.

4. Cohort 1: Patients with operable or borderline operable resection, scheduled for primary lesion resection and peripheral lymph node dissection, and suspected presence of peripheral lymph node or distant metastasis; The pathological results of the primary lesion and lymph node dissection were obtained.

   Cohort 2: Patients with confirmed or suspected postoperative recurrence or advanced metastasis by routine imaging had at least one measurable lesion; Patients who can undergo imaging follow-up for 3 to 6 months or can undergo pathological biopsy.

5. The ECOG score is 0-2

6. Patients with adequate organ function.

Exclusion Criteria:

1. Previously received FAP-targeted radioligand therapy.
2. Patients are participating in any other clinical trials or receiving investigational drugs.
3. Patients with central nervous system (CNS) metastases with symptoms or receiving glucocorticoid therapy to maintain functional integrity of the nervous system.
4. Patients with other malignancies that may interfere with disease assessment, who have a prior history of malignancy but have been adequately treated, who have not been treated for more than 3 years prior to enrollment, and who have no evidence of recurrence are eligible to participate in the study.
5. Comorbidities with serious or poorly controlled medical conditions, including but not limited to hard-to-control infections, known active hepatitis B or C, or other conditions that investigators believe may impair study participation or collaboration.
6. A physical or psychiatric history that may interfere with the purpose and evaluation of the study, or any condition in which the investigator determines that the patient is incapable of cooperating with imaging and procedures.
7. Patients who do not consent to effective contraception or restricted sexual practices.
8. There are other conditions that the investigator deems unsuitable for participation in the trial.