The oncologist said he's usually comfortable discontinuing the diphenhydramine after the tumor is removed and found to be low grade. Just in case, I am planning on continuing it until at least her next several rechecks if the abdominal u/s and aspirates come back fine. We're definitely continuing the famotidine too for her GI ulceration. Right now, we're thinking that the vomiting blood/GI ulceration might have been a red herring. She had a similar episode a year ago, so we're still unsure of the cause. Both episodes were during times of increased stress and when her separation anxiety was really flared up, so the current theory is that she had some stress induced gastric ulceration. I chose famotidine over cimetidine for a couple of reasons. First, she is nearly impossible to pill. She gets wise to hiding pills in literally anything. It only works once, and then she treats anything you give her (including her food) like it's poison. She is easily the most difficult animal I've ever pilled. I swear she can hide pills in her esophagus for five minutes before spitting them up when I'm not looking. Right now I'm having to give her 10 separate pills a day, which can get incredibly frustrating. Famotidine is once daily, while cimetidine is multiple times daily dosing. I know that doesn't exactly seem like the best reason, lol, but I'll take whatever relief I can get! It is also more potent than cimetidine, and I've read a couple studies claiming it is more effective. Cimetidine also inhibits hepatic cytochrome P-450 drug metabolism pathways, while famotidine does not. So cimetidine can increase the pharmacological effects or toxicity of many drugs (like benzodiazepines, antidepressants, beta blockers etc). We're currently trying Zylkene for her anxiety, but if that doesn't work, we may move her to something like fluoxetine, and the last thing I want to worry about is drug interactions. Have you had dogs with mast cell tumors? If so, what was the ultimate outcome for them? The elation that the histopath report brought today has kind of faded, and now I'm back to worrying (it's what I do best) about recurrence, lurking mets, and survival times.