Tumor in belly.

I recently discovered my 13 year old cat has a probably cancerous mass growing in her stomach. I am at odds with myself about how to proceed.

I took her to the vet when I noticed a half dollar size sore on her back. The vet was concerned this may be cancer because of the thickness and hardness of the sore and recommended surgically removing it.

But then as she was feeling around in my cat’s stomach she felt a rather large mass inside. My cat layed calmly on the table as the vet gave a firm and thorough examination with her hand, but afterward my cat made horrible meowing noises and made a face I had never seen on a cat that could only have been from awful pain.

The vet then took x-rays to see the extent of the mass. The x-ray showed what looked like a baseball sized mass in my cat’s stomach. The mass seemed to be pushing up her intestines. One of her kidneys were shrunken almost to the point of non-existence. The vet also seemed concerned about some almost invisible white dots in the lower lung area.

The vet wants to do an ultrasound to see where exactly the mass is situated and if it is operable. Even if it is operable, the mass may have mestasized which means the surgury would not be enough to cure her. How likely is it that the sore on her back is caused by the mass in her stomach spreading?

If I were to forego treatment, I wonder if the sore poses a risk of infection? The vet gave my cat an antibiotic shot just in case, but that only covers a couple weeks. I also wonder about her comfort level down the road. She seems to be content at this point since I have not noticed any signs of pain since her check up. She eats normally, follows me around the house and purrs as usual. The only thing wrong with her is that she does walk in an arthritic-like style, but she has been doing that for about a year and I am giving her “Hip and Joint” treats with Glucosamine to help. Also, the vet said her blood panel showed that she was a bit anemic, which is likely because of the mass in her stomach.

If I forego treatment what would her future outlook likely be? And if I were to treat her (surgury, etc), what should I expect of her future?

Thanks for your advice.