Thanks for the additional information...when I re-read your initial post I saw that you had mentioned it was a sarcoma. I apologize...I must have missed it the first time...
First and foremost, I'm sorry to hear that your dog, was diagnosed with this kind of sarcoma. This is, unfortunately, one of the most aggressive forms of cancer and the one with the poorest prognosis.
As a general rule of thumb, sarcoma can spread rather quickly. At our clinic, we tell clients that a dog with a confirmed case of sarcoma has, if left untreated, a life expectancy of about 12-26 months from the time of diagnosis. Of course, we can TRY to extend that with chemotherapy and/or radiation therapy, however in an older dog that time would be drastically reduced.
Because this is such a common neoplasia, there is a ton of information out there to help you understand what is going on:
That being said, just like humans, every dog is different and of course, if you're not sure how to procced, then it might be a good idea to ask your vet for a referral to a veterinary oncologist. I think if this were my dog, I'd ask for the referal. They'll run even further testing to ensure that this is, in fact, sarcoma. Once you get a second confirmed diagnosis, you can figure out how to treat this and which course of action is best for your dog.
Sadly, just like in humans, there aren't any holistic 'cures'. However, some people swear by the canine cancer diet. You can read more about it here:
You're already doing a great job of supplementing your dogs nutritional and health needs. Hopefully using the cancer diet as well will give you more time with your companion.
I hope this helps.