Molecular residual disease (MRD) has strong relationship with clinical outcome in multiple solid tumors. Here, the investigators try to verify the negative predictive value of undetectable MRD, which is considered as a superior prognostic factor for resected NSCLC patients, and not requiring excessive adjuvant therapy. Stage IB-IIIA resected NSCLC patients with landmark and longitudinal undetectable MRD are enrolled and under close surveillance in this study.

Stage IB-IIIA resected NSCLC patients will undergo two-round MRD tests after operation, first in 3-7 days and second in 1 month after operation. And patients who confirm two-round landmark undetectable MRD will be enrolled. Enrolled patients will be under close MRD and imaging monitoring without any adjuvant therapy.

Inclusion Criteria:

• Stage IB-IIIA non-small cell cancer patients who after complete resection.
• ≥18 years.
• Two-round MRD tests confirm landmark undetectable MRD.
• Expected survival ≥12 weeks.
• Expected survival ≥12 weeks.
• ECOG PS 1-2.
• Willing to accept MRD monitoring every 3 months for a total of 2 years after operation.

Exclusion Criteria:

• Patients who had previously undergone radiotherapy or chemotherapy or any other anti-tumor therapy.
• Patients with a history of other malignancies in the past 5 years.
• Any unstable systemic disease (eg, active infection, high-risk hypertension, unstable angina, congestive heart failure, etc.).

Stage IB-IIIA NSCLC patients who after complete resection and undetectable landmark MRD.