The basic treatment is amputation followed by Chemotherapy. If more than one limb is affected and/or the owner does not elect amputation, then Chemotherapy alone.

Osteosarcoma reference

This reference lists the combo of Carboplatin, and Doxorubicin. The Carboplatin has a high probability of severe nausea and the dog should be pre-treated, and treated for a couple days afterward with Zofran (expensive). The Doxorubicin my Lymphoma puppy never had much problem with. I gave her Metoclopromide (cheap) and Cimetidine to counter any nausea. Coenzyme-Q administration helps decrease the cardiotoxicity of Doxorubicin per human trials.

Osteosarcoma is very responsive to anti-angiogenesis drugs which for the most part are still coming online for humans. An older try in dogs is the :

Navy Protocol

Start supplementing the dog's diet with fish oil. The Omega-3 fatty acids have a mild anti-angiogenic , and a mild anti-inflamatory effect. Stay away from as much carbohydrate in the diet as possible - no more ice cream at night!

The latest research indicates the bisphosphonates (e.g. Fosamax) which is primarly used to prevent bone reabsorption in geriatric humans, definitely slows down the Osteosarcoma in the bone, lessens bone fractures, and pain. Ask for it as a supportive treatment! It can be pricey.

Good luck to your friend's puppy and its upcoming struggle against cancer.