I definately would take her to the vet. Cassie has a few of the fatty tumors in her abdomen and chest. The vet told us that older dogs get them. She had one on the side of her face for over a year. We thought it was a fatty tumor, too, until it burst over Memorial Day weekend. Ended up, it was a cyst that had been festering for a long time and was full of infection. She had surgery to remove it, and she was a different dog in 48 hours....feeling so much better, eating better, more energy. We won't assume anything anymore. More than likely, they are some sort of fatty tumors or subaceous (sp?) cysts. All are harmless and very common according to our vet.