I'm sorry to hear. I hope it's nothing serious but even if it's a mast cell don't panic. My Ginger had one removed on her neck about 2.5 years ago and she has been fine. Most of the time they are localized and can be removed completely. I will send prayers for Nebo that it's nothing serious and even if it is a mast cell they they remove it with clean margins. Most often, especially if caught early, they can be removed without furhter harm. Try to hold onto that hope and don't despair, I know it's scary I've been there. Good luck and let us know.