The purpose of this prospective study is to compare the diagnostic utility of two techniques (brush cytology + FISH and brush cytology + free DNA analysis) in the diagnosis of biliary strictures. Histologic diagnosis (biopsies) in conjunction with clinical and/or imaging follow-up will serve as the gold standard for diagnosis of malignancy. In order to do this the investigators will ask study participants to have a small volume of fluid obtained from the bile duct sent for additional testing at RedPATH. In some patients additional brushings will be obtained for FISH testing (this adds <2 minutes to ERCP and only associated risk is increased procedure duration).

The investigators hypothesize that the use of cytology +DNA analysis has a higher sensitivity and accuracy when compared to cytology +FISH in patients with biliary strictures.

Primary aim:

To compare the sensitivity and accuracy of the two techniques (brush cytology + FISH and brush cytology + free DNA analysis). Histologic diagnosis (histology from biopsy or cytology for fine needle aspiration) in conjunction with clinical and/or imaging follow-up will serve as the gold standard for diagnosis of malignancy.

Secondary aims:

1. To evaluate the diagnostic yield of malignancy when all three techniques (cytology, FISH and DNA analysis) are used.
2. To evaluate the added value of biliary forceps biopsies, when used in conjunction with cytology, FISH and DNA analysis.

Inclusion Criteria:

1. Patients age: > 18 years
2. Presence of a biliary stricture
3. Ability to provide written informed consent.

Exclusion Criteria:

1. Severe coagulopathy (INR > 1.8) or thrombocytopenia (platelet count <50,000)
2. Inability to cannulate the common bile duct
3. Presence of altered anatomy (Billroth II or Roux-en-Y reconstruction)

Patients over the age of 18 undergoing ERCP for the diagnosis and treatment of bile duct stricture