Where to start? Just start making appointments.
I realize it's emotionally overwhelming, and you are hoping that the tests come back negative and that the vet is wrong. Just start making appointments. You can cancel them. But most vets, oncologists, holistic vets, etc have 3 weeks or longer wait times. Ask what the cancellation policy is and what the cost for a consult is.
It's easier to cancel an appointment than to wait until you are emotionally ready to book them.
Other places to start:
-Call your pet insurance company to ask what is covered/not covered
-Search Facebook for groups and start posting asking for help
-Post on Facebook asking for books or blog recommendations
I started this blog so that when a friend texts me asking me to talk to someone whose dog just was diagnosed with cancer, I can send them this website. Check out my PDF downloads as well.