Tilly, a stoic collie, presented to us at West Midlands Veterinary Referrals with whopping cancer on her leg. This was thought to be composed of fatty tissue from samples that had been taken by the referring vet, but the mass looked so unlike typical fatty masses that we double-checked with biopsies. Indeed it was of fatty tissue origin. Fatty masses are usually benign, but the possibility of infiltrative or malignant variants was strongly suspected.