Delayed Systemic Therapy Following Destructive Local Treatment of Pulmonary Oligometastases After No Evidence of Disease (NED) in Colorectal Cancer.

Inclusion criteria

• Patients with a pathologically confirmed diagnosis of colorectal cancer with the following disease conditions:
• The patient has achieved No Evidence of Disease (NED) after undergoing EMR, surgery, radiofrequency ablation, or radiotherapy.
• NED has been maintained for ≥ 6 months.
• The patient has not received chemotherapy, or has only received postoperative adjuvant chemotherapy or first-line systemic therapy.
• Oligometastatic lung lesions (defined as 5 or fewer lesions) detected after ≥ 6 months of NED maintenance, eligible for destructive therapy.
• No prior radiotherapy to the lungs.
• RECIST 1.1 criteria: The patient must have measurable lesions, defined as at least one nodal lesion with a longest diameter \> 1.5 cm, or at least one nodal lesion \> 1 cm with an accurately measurable pendulous diameter.
• ECOG performance status: ≤ 2 (Eastern Cooperative Oncology Group general condition score).
• The patient's expected survival must be ≥ 3 months.
• Adequate hematologic function: Absolute neutrophil count ≥ 1.6 x 10⁹/L, with no growth factor support for at least 7 days prior to testing.
• Normal organ function: The patient must be able to tolerate at least one of the local destructive treatments, as assessed by the corresponding department's physician, based on normal hepatic, renal, pulmonary, and cardiac function.
• Reproductive age: Female patients of childbearing potential must agree to use a reliable method of contraception with their partner from the time of informed consent until 1 year after treatment completion.
• The patient must have voluntarily provided informed consent to participate in the study.

Exclusion criteria

• First diagnosis of advanced colorectal cancer with metastatic disease.
• Multiple lung metastases (\> 5 lesions), liver metastasis, bone metastasis, or lymph node metastasis.
• Lung metastases that are not amenable to radiotherapy, as determined by the investigator.
• Previously received second-line or higher systemic treatment.
• Liver or kidney dysfunction: Alanine aminotransferase (ALT) \> 3 times the upper limit of normal; Aspartate aminotransferase (AST) \> 3 times the upper limit of normal; Total bilirubin (TBIL) \> 2 times the upper limit of normal; Serum creatinine \> 1.5 times the upper limit of normal.
• Elevated tumor marker: CEA ≥ 50 ng/mL.
• Serious medical conditions that may interfere with the study (e.g., uncontrolled diabetes, gastric ulcers, severe cardiopulmonary diseases), at the discretion of the researchers.
• Severe or uncontrolled infections.
• Active autoimmune disease.
• Clinically significant central nervous system dysfunction.
• Recent major surgery (excluding lymph node biopsy) within the last 30 days.
• Pregnant or breastfeeding women of childbearing age who are not using contraception.
• Drug allergy to study treatments.
• Other reasons, as determined by the researchers, that make the patient unsuitable for participation.