Foot lumps are soft-tissue masses (not bone) that can occur anywhere on the foot. They can be caused by soft-tissue swelling, sacs of fluid, fatty tissue and nerve, vessel or muscle enlargements. Foot lumps may be without pain (asymptomatic), or they can cause pain and affect the function of the foot. Painful foot lumps can be treated by a foot and ankle surgeon using a variety of conservative treatments. In some cases, surgery may be necessary.