Suspected Cholangiocarcinoma, Repeated Negative Biopsies

My 73-year-old father has suspected perihilar cholangiocarcinoma. We've seen 2 experienced hepatobiliary surgeons who strongly suspect locally advanced cancer due to blood vessel involvement and therefore suggest chemo (not surgery).

Despite multiple ERCPs, brushings, and biopsies, we still don't have a definitive diagnosis. One brushing showed atypical cells, CA19-9 remains elevated, and FISH results are pending.

The doctors won't begin treatment without a confirmed diagnosis and I'm afraid we are losing time.

1. How did you finally get a diagnosis after negative biopsies? Were any particular tests helpful?
2. Which doctors or teams at Mayo Rochester would you recommend?
3. Has anyone started treatment without a positive biopsy?

We've requested an appointment at Mayo and are hoping to move quickly. Any advice or recommendations would be greatly appreciated!