Are major cancer centers better option to get into clinical trials?

I don't know the U.S. health system first-hand, but in general, it is a good idea to get to a facility that's affiliated with a big university medical school, where the oncologists also conduct research and teach as adjunct professors.

Hi @anon0 As @northoftheborder mentioned, often clinical trials are affiliated with larger university medical schools or medical institutions such as Mayo Clinic.
Because clinical trials require registration and oversight, the National Institute of Health (NIH)-National Cancer Institute has a website making it possible to search for current (future and past) clinical trials.

Here’s a link to their site:
https://www.cancer.gov/research/participate/clinical-trials/disease/breast-cancer
Wishing you well in your quest! Will you let me know what you find out, please?

Definitely yes. Major centers also have multiple protocols or clinical trials that you might qualify to enter. While smaller less experienced center staff may disqualify you on some small “technicality” that they read from a rigid rule book, staff at bigger experienced centers may view the same parameter from a more “relaxed” viewpoint.