I will name what is possibly the type of cancer. I will list f possible cancers your dog might have.
1. Lipomas and Liposarcomas
Lipomas are tumors of fat that appear on older females. Dobermans Pinschers, Labrador Retriever, Miniature Schnauzers, and mixed breed dogs.They may seem to grow (or stay small).Surgical removable is the cure. Infiltrative lipomas are rare in dogs, but are most common on middle aged females, on their chest or legs. The breeds listed above are victims to this cancer. They can be very soft. Invasive lipomas appear on the legs . The limb affected may have to be amputated.
2. Lymphoid Tumors of the Skin
Canine extramedullary plasmacytomas appears on the ears, lips, mouth or legs on middle aged dogs. They mainly affect Cocker Spaniels, Airedales, Scottish Terriers, and Standard Poodles. The tumors are small (less than 2 inches). Epitheliotropic lymphosarcoma are found in middle aged dogs (Poodles, Cocker Spaniels), and may appear on footpads. No treatment has been found to be very successful.