Hello! My name is XXXXX XXXXX it will be my pleasure to help you with your dog today.
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.
It seems your dog actually has two different problems. First, let's look at the spindle cell tumor: With Spindle Cell growths, the best course of treatment is a radical surgical excision where they whole tumor is taken out, as well as a fairly large amount of normal tissue around the area. If this is done, then a cure is very possible. Of course, if the entire growth isn't removed, or if the planes around it aren't adequately removed, the tumor will likely grow back, and will probably grow back deeper and stronger. Sometimes vets use radiation or chemotherapy to treat and view 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:
Although there is no for sure cure, there are some people swear by the canine cancer diet. You can read more about it here:
I hope this helps.