The goal of this observational study is to detect the methylation characteristics of cfDNA in the bile and plasma of patients with bile duct stricture. The main question it aims to answer is: Can the developed model, using peripheral blood and bile cell-free DNA sequencing, work well in screening and classifying unknown biliary stricture? Participants will collect approximately 10ml of peripheral blood and 5ml of bile from the patient.

Inclusion Criteria:

• 1. Patients with biliary stricture aged between 18 and 90 years old.
• 2. Patients scheduled to undergo ERCP surgery due to obstructive jaundice or cholangitis.
• 3. Definite benign or malignant diagnosis: with a pathological diagnosis of benign or malignant disease, or with follow-up data indicating a benign or malignant diagnosis.

Exclusion Criteria:

• 1. Receive radiotherapy, chemotherapy, or targeted therapy before sampling.
• 2. Malignant tumors in other parts of the body (not related to biliary stricture).
• 3. Unable to determine the nature of the biliary stricture.
• 4. Ineligible for ERCP due to systemic conditions or gastrointestinal obstruction.
• 5. Pregnant or breastfeeding women.
• 6. Unable to sign the informed consent form.

According to the "Sample Size Calculation for Comparative Diagnostic Studies with Categorical Variables (Rates)" method, it is calculated. Based on the previous research results, it is estimated that the diagnostic sensitivity of sequencing methylation profiles in bile cfDNA is 82%, the specificity is 95%, the allowable error in sensitivity is 0.1, the allowable error in specificity is 0.1, α is set to 0.05, the loss to follow-up rate is 10%, and the calculated sample size is approximately 161 cases.