Because I've been using two treatments simultaneously, I can't be sure which has been most effective in shrinking the melanomas. The melanoma under Katie's tail has shrunk by 50% at this point, the anal melanoma is visually imperceptible, and the melanoma on her teats remains unchanged. From what I've read and gleaned from conversations with veterinarians, melanomas are rarely fatal in a horse. I will continue to administer the Cimetidine for another three months, then discuss its continuation with my veterinarian.