What Causes Elbow Swelling With Bruising?

bruised and swelling elbow. i havent banged it, it has been sore for awhile but its hurtin alot the last few days and now it is very badly bruised.. i was thinking it is tennis elbow but could it be cancer because my mum knew someone a long time ago who was told they had tennis elbow but few weeks later was told it was cancer. i will be going to hospital tomorrow to be checked out but i am worried about what the outcome maybe.. please could you advise me your thoughts on how and why my elbow is swollen and bruised for no apparent reanson.. ..