Your family veterinarian is the best place to begin. Often your veterinarian will consult with or refer you to oncology specialists. Exactly which you need will depend on the type of diagnostic procedures as well as the potential treatment options you want to discuss. Diagnostic oncologists are more common than radiation oncologists who perform radiation treatment. So you might end up seeing several veterinarians in several locations. If you are near one of the top oncology research universities you might find them all on one campus.
American Veterinary Medicine Association: Note that not all veterinary colleges have oncology departments. https://www.avma.org/education/accredited-veterinary-colleges
Association of American Veterinary Colleges: https://www.aavmc.org/about-aavmc/our-members/
American College of Veterinary Radiology: https://acvr.org/find-a-specialist/ Note that this website includes diagnostic oncologists as well as treatment radiologists. Not all will be able to perform radiation treatment therapy.
Veterinary Cancer Society: http://vetcancersociety.org/pet-owners/find-a-vcs-member/
American College of Veterinary Surgeons: https://www.acvs.org/
Veterinary Cancer Society: http://vetcancersociety.org/pet-owners/find-a-vcs-member/
Private Corporate Oncology Clinics:
One Health Company: https://www.fidocure.com/find-a-clinic
Look for Clinical Trials near you: http://vetcancersociety.org/pet-owners/clinical-trials/ Note that clinical trials are usually very specific about what type of cancer and dog the study is following. Some clinical studies cover all costs, some require some portion of costs to be paid by dog's caregiver.
PennVet University of Pennsylvania Handouts for Oncology Clients: https://www.vet.upenn.edu/veterinary-hospitals/ryan-veterinary-hospital/services/comprehensive-cancer-care/information-for-clients/information-about-cancer
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