Hi again - I think it's pretty standard to get a 2d opinion on cancer treatment, and I'm guessing your oncologist wouldn't object to a request for a referral to an expert s//he has a good relationship with.
I have stage IVB endometrial cancer with mets to the lungs. My onc asks all of his gyn cancer patients to get a 2d opinion from Dr Armstrong (she's only 1 hour away at a top comprehensive cancer center). He has an excellent working relationship with her and trusts her to recommend patient-specific treatment for the present and future.

I was able to get an appt within 2 weeks. She spent plenty of time with me reviewing everything. She and her team produced a multi-page report confirming that my current treatment is gold standard, and outlining approaches to take in the future should my condition change. The facility was top notch (I think they all are) and parking in the building was surprisingly cheap! (Cheaper than my suburban onc's office park. For some reason, expensive parking irks me.)

Of course, you have excellent cancer centers a bit closer to you in Philadelphia. But I just thought I would add my personal experience in a location not that much farther from you.