The goal of this clinical trial is to explore the value of molecular residual disease (MRD) monitoring based on ctDNA in advanced or metastatic pancreatic cancer. The main questions it aims to answer are:

• prognostic value of baseline MRD;
• the role of MRD dynamic changes after treatment in guiding treatment. Peripheral blood derived from participants will be obtained for MRD test before first-line chemotherapy initiation and at the first imaging assessment after chemotherapy.

Inclusion Criteria:

• patients with histologically confirmed unresectable advanced or metastatic pancreatic cancer;
• both sexes, age ≥18 years old;
• ECOG performance status score ≤2;
• the expected survival time was ≥3 months.

Exclusion Criteria:

• a known diagnosis of pancreatic cancer other than ductal adenocarcinoma;
• treated with any systemic antitumor treatment before first-line chemotherapy onset;
• died or lost to follow-up within one month after the initiation of first-line chemotherpay;
• combined with other primary malignances.