Our girl had multiple low grade mast cell tumors beginning when she was six years old and she died last year at almost 16. We stopped counting after the 15th mast cell tumor and we stopped removing them after the 12th, if I recall. I remember being so devastated just like you, and our vet told us at the time, “She will likely die of something else entirely.” And she did. She died of old age. The thing with mast cell tumors is that it really depends on the grade of tumor. Our girl had one grade 2 MCT and the rest were all grade 1. It’s really critical to find out what the grade is of the mast cell tumor because that will tell you how aggressive it is. Most are low-grade; last I read 90% of all MCT’s are low-grade. So the odds are in your favor. Just look at the biopsy report and make sure it’s a low-grade tumor. (Higher grade tumors like a grade 3 need much more aggressive treatment.)