Dear Mary: Hematomas are basically bruises that usually occur as a result of some injury. They do not cause cancer. Sometimes a hematoma may have to be drained, but they usually resolve on their own. This can take a long time, however.
you cannot get cancer from a hematoma. Rarely, there could be bleeding within a cancer that could cause a hematoma; but in most cases by far, the hematoma is from a known injury. In the vast majority of cases, they will go away on their own; sometimes it's necessary to drain them. And there's a small risk that they can get infected before they go away. The standard treatment, however, absent signs of infection is applying heat if possible, and give it time.