• Age ≥ 18 years, no gender restriction;

• Histopathologically confirmed diagnosis of advanced, metastatic, or recurrent malignant tumors, primarily including colorectal cancer, esophageal cancer, gastric cancer, pancreatic cancer, lung cancer, and cholangiocarcinoma;

• Failure of at least second-line standard treatment (disease progression or intolerance, such as surgery, chemotherapy, radiotherapy, etc.) or lack of effective treatment options;

• Immunohistochemical staining of tumor samples showing CEA positivity (clear membrane staining, positivity rate ≥ 10%) within the past 3 months; if the immunohistochemical result is older than 3 months (clear membrane staining, positivity rate ≥ 10%), serum CEA must exceed 10 µg/L;

• At least one evaluable lesion according to RECIST 1.1 criteria;

• ECOG performance status of 0-2;

• Expected survival of ≥ 12 weeks;

• No severe psychiatric disorders;

• Unless otherwise specified, the following important organ function criteria must be met:

∙ Hematology: White blood cells \> 2.0 × 10\^9/L, neutrophils \> 0.8 × 10\^9/L, lymphocytes \> 0.5 × 10\^9/L, platelets \> 50 × 10\^9/L, hemoglobin \> 90 g/L;

‣ Cardiac function: Echocardiogram shows ejection fraction ≥ 50%, ECG shows no significant abnormalities;

‣ Renal function: Serum creatinine ≤ 2.0 × ULN;

‣ Liver function: ALT and AST ≤ 3.0 × ULN (can be relaxed to ≤ 5.0 × ULN for patients with liver tumor infiltration);

‣ Total bilirubin ≤ 2.0 × ULN;

‣ Oxygen saturation \> 92% without supplemental oxygen;

⁃ Eligible for single or venous blood collection, and no contraindications for cell collection;

⁃ The subject agrees to use reliable and effective contraception methods from the time of signing the informed consent form until 1 year after CAR-T cell infusion (excluding rhythm method);

⁃ The subject or their authorized guardian agrees to participate in this clinical trial and signs the informed consent form (ICF), indicating understanding of the trial's purpose and procedures and willingness to participate in the study.