We had a beloved dog who had Osteosarcoma, as she was approx approaching 12 yrs, at that time chemo wasn't an option given, only amputation of the limb.
She was diagnosed early, but after speaking to the chief vet, we decided on palliative care and home visit by vet for euthanasia when the time was right {within weeks of diagnosis}.
However... In a young dog, and 6 is still ''Young'', and I've read that 'Chemo' side effects in dogs is not as bad as humans.
Every case surely has to be considered own it's merits.. I do know of two hound types, one 12 and the other 6 who have had amputations and chemo, and {Touch wood} they are alive more than a year after diagnosis.
They appear to be enjoying life {From social media posts anyway}
Best wishes to your poor dog....and to you.
A vet is really the only person able to give proper advice...randoms like me can only give 'Anecdotal evidence'.
An American FB group I was on specifically for Osteosarcoma I had to leave{I'm in UK}, as it was just so utterly awful to witness the selfishness of the owners in some instances.
Owners would ask ''what can I give for vomiting and coughing and crying'?'' .......people would chorus ''CBD oil and lavender''
videos would be posted of grotesquely limping dogs with distorted limbs, with ''Kicking cancer's butt'' in the comments.
Dogs hide their pain so well when very ill... it was clear that many of these owners put their own needs before the dog, in that they would rather have the dog in any condition than not at all.
This is definitely the worst part of being a pet owner, having to make these decisions.