My Lab, Lena, who's 7 has a nasty tumor on her right back hock. I noticed it about two weeks ago and it's gotten bigger rapidly. Took her to the Vet yesterday and my worst fears were confirmed- not a cyst, a solid mast cell tumor. The Vet took a sample, microscoped it and said the cells were just multiplying like crazy. Great. She took a sample from the lymph gland that is about 1" from the tumor and it appeared clear. Hopefully it hasn't spread. Mast cells are notoriously aggressive and unpredictable. I'm taking her in on Friday morning for the tumor removal. Hopefully it'll be a Good Friday! She's such a great dog and my son's world revolves around her. Say a prayer if you'd like, we'd sure be appreciative.