I have a very elderly Arabian mare; she's grey and has had melanomas on her dock and around her perineum for the past 7 or 8 years. They have always been just normal, hard tumors until last winter, when one of them on her dock (about the size of a golf ball) started to shed off layers of tissue, like dry and flaky. Last week this same tumor started to come apart in chunks, and under each chunk that came off was a pocket of pus. The tumor is now soft and about half the size it was due to pieces coming off, looks like cauliflower, and is oozing pus from the indentations. It does not seem to bother her at all, I have been keeping it clean and disinfected with hibitane scrub and that yellow furazone spray once it has dried, and the infection seems to be clearing up. But what is going on here? How does a seven year old tumor suddenly become a ball of pus? Do tumors abcess? Has anyone else had this happen?