A hard bump on the foot may be considered a tendon sheath cyst or a lipoma. A tendon sheath cyst is a mass on a tendon that is wrapped in a membrane on the outside, and the membrane is very hard in texture with a cystic fluid on the inner surface. Tendon sheath cysts can move up and down with the movement of the tendon and are very hard and well defined when pressed, and can move up and down from side to side. Small tendon sheath cysts may not require surgery for a while because they may rupture on their own after a long period of time. If the cyst is long, or if it is large and painful, then surgery may be considered. Lipoma is a mass formed by abnormal growth of subcutaneous fat, which is usually softer in texture, with fat inside, and is also a benign lesion. Small lipomas can be followed up, but if the lipoma is large and affects the appearance, surgery can be considered to remove it.