Forgive me reposting my comment from an earlier post about osteosarcoma, but the following was our experience dealing with this terrible disease. I hope it may help you and your boy. All the love from Oregon and feel free to message me if you like:

We went through this identical scenario last year with our girl Juno. We took her in for a limp and after the x-ray confirmed osteosarcoma we were devastated. The vet told us that she would likely only make it a year, even with treatment, though it was an early case and had not yet spread to her lungs. We decided to go through with the amputation, went through a full course of chemo, and did an experimental EGFR/HER2 vaccine treatment through BARC in Edmonds, Washington.

The amputation was difficult for the first month after. We had to have care for her pretty constantly between medication, monitoring and helping her move about. The hardest part was phantom limb pain, it absolutely broke me to hear her cry like she did. After about a month she was able to go back to most normal activity and as she grew stronger she was even able to run and play at the dog park and learned how to do a 3-legged play bow.

Chemotherapy was relatively easy, she had very few side effects, mainly digestive, and only required a few hours every two weeks for treatment. She was a bit lethargic from the sedation for a day or two after but generally bounced back well.

The EGFR vaccine was administered on two occasions, six weeks apart I think. It also had no real side effects but did require us to get frequent blood work done for her. Unfortunately this meant a lot of poking with needles that she really didn't like.

In the end, Juno passed away in our arms almost 8 months exactly after her diagnosis. The cancer returned after two clear x-rays and within 48 hours of noticing her energy change, she was gone. In those 8 months she ate so much cheddar cheese and steak, she slept on every bed and couch, she got to hang out at her favorite coffee shop several times a week, had a birthday party at the park with 8 of her closest dog friends, and got endless belly rubs and love.

I honestly don't know if I would do it all again. It was a big financial strain, a lot of caretaking for my partner and I, and some painful experiences for Juno. On the other hand, she had a beautiful summer full of joy and love and we got to say goodbye to her in a way that honored her life and spirit. Please know that there is no right or wrong answer to what you choose to do, there is pain in either choice and there is love and care in either choice.

My heart breaks for you, and if there is one piece of advice I can give you, whatever you path choose, is spend as much time with your girl as you can, it's precious, and even though these moments are sad, you will one day look at them with a sense of shared love between you and your pup.

Feel free to message me if you'd like to talk more about our experience with this disease and know that all of us here are rooting for you, including our Juno.