Inclusion Criteria:
1. Aged ≥ 18 years, regardless of gender.
2. Gastric cancer and colorectal cancer that are inoperable and unresectable with radiotherapy: For gastric cancer, molecular diagnosis confirms that it is not AFP-producing gastric cancer.
3. Progressive disease or recurrence after receiving ≥ 2 lines of treatment.
4. Patients are divided into two groups (Group A and Group B) based on the presence or absence of peritoneal metastasis. The criteria for determining peritoneal metastasis are as follows:
1. Drained ascites ≥ 500ml, or B-ultrasound/CT in the supine position shows ascites depth ≥ 3cm.
2. Peritoneal metastasis confirmed by any of the following criteria:
i. Positive for exfoliated cancer cells in ascites. ii. Diagnosed as peritoneal metastatic carcinoma by imaging and symptoms. iii. Peritoneal metastasis confirmed by abdominal exploration. iv. Ascites confirmed as exudate by routine ascites examination and ascites biochemistry.
5. At least one measurable lesion on CT or MRI according to RECIST v1.1 (Response Evaluation Criteria in Solid Tumors).
6. ECOG performance status of 0-2.
7. Expected survival period ≥ 3 months.
8. Able to comply with the study protocol and follow-up procedures, and voluntarily sign the informed consent form for participation in this study.
Exclusion Criteria:
1. Pregnant or lactating women.
2. Subjects with central nervous system (CNS) metastases and/or carcinomatous meningitis with obvious symptoms.
3. A history of other malignant tumors within the past 3 years.
4. Subjects with active, known or suspected autoimmune diseases \[excluding type 1 diabetes, hypothyroidism requiring only hormone replacement therapy, skin diseases that do not require systemic treatment (e.g., vitiligo, psoriasis, or alopecia), or diseases that are not expected to relapse without external triggers\].
5. Subjects with a history of immunodeficiency, including positive HIV test results, other acquired or congenital immunodeficiency diseases, or a history of organ transplantation.
6. A history of severe cardiovascular and cerebrovascular diseases, including but not limited to: severe cardiac rhythm or conduction abnormalities such as ventricular arrhythmias requiring clinical intervention, third-degree atrioventricular block, etc.; QTc interval \> 480 ms on 12-lead electrocardiogram at rest; acute coronary syndrome, congestive heart failure, aortic dissection, stroke, or other grade 3 or higher cardiovascular and cerebrovascular events within 6 months before enrollment; New York Heart Association (NYHA) cardiac function classification ≥ class II or left ventricular ejection fraction (LVEF) \< 50%; clinically uncontrolled hypertension.
