I am an IV user. I inject into the veins in my breast. A week ago I did a shot and got a great flow so I know I was in a vein but when I plunged it burned and a rash apeared for a few hours. It bruised a few days. Now the bruising is gone but there is a painful hard lump in my breast. I don't think its an abcess because its not red or hot. There is just a painful lump. Could I have caused cancer?