A fatty lump most often situated between the skin and underlying muscle layer. Lipomas are slow growing and usually harmless. Rarely, they can be cancerous. Some people have more than one. Lipomas are just under the skin and move easily when pressure is applied. They commonly occur in the neck, shoulders, back, abdomen, arms and thighs. Treatment generally isn’t necessary, but if the lipoma is bothersome, painful or growing, surgical removal may be required.