1. To verify that thalidomide can increase the efficacy of cetuximab plus chemotherapy in the treatment of stage IV RAS and BRAF wild-type unresectable left colorectal cancer, which has important clinical significance and provides a basis for subsequent large-scale research and clinical application.
2. To evaluate the changes of cytokines and verify the effect of some cytokines on the efficacy of cetuximab +FOLFIRI, so as to provide a scientific basis for the subsequent precise therapy using cytokines antibodies.

Inclusion Criteria:

1. Patients with RAS and BRAF wild-type IV unresectable left colorectal cancer confirmed by pathology and tissue/cytology and genetic testing;
2. Physical state is good: PS 0-2;
3. Expected survival of more than 3 months;
4. Aged 18-75 years old;
5. Have not received systematic chemotherapy before;
6. Did not receive cetuximab treatment;
7. Liver, kidney and bone marrow functions are basically normal;
8. The clearance period of chemotherapy and molecular targeted therapy is more than 4 weeks;
9. Voluntary participation in the group, good compliance, can cooperate with the experiment observation, and sign the written informed consent.

Exclusion Criteria:

1. Patients with severe dysfunction of vital organs (heart, liver, kidney);
2. Patients with other malignant tumors;
3. Patients who are pregnant or breastfeeding (women of childbearing age need to check pregnancy test);
4. In the active phase of acute or chronic infectious diseases;
5. People with a clear history of drug allergy or allergic constitution;
6. Patients participating in other clinical trials;
7. Other conditions in which the patient was considered inappropriate to participate in the study.