I've got a small lump on left foot on top.is not painful.no swelling.?

A few things: It sounds like it could be a little bursa, ganglionic cyst, lipoma or if it is hard, a bone spur or prominence of bones at the top of the foot. Keep an eye on it. If it gets bigger, painful or shows sign of shoe irritation consider seeing a podiatrist.

Cancer does not : Have to cause pain or swelling. If you have a lump it can be benign like a ganglion but it can also be a form of cancer like a synovial sarcoma. Lumps should be biopsied. Always err on the side of caution.