Most of the the time cancer sneaks up on people in different ways than just a discharge. For instance, cancer in the breast is a hard lump you feel that has no pain. You would think it would be painful being cancer but it is painless.
You may have cystic breasts with this fluid. Get a 2nd opinion from other doctors. It depends on what you're taking too. Are you on hormone replacement therapy? Try browsing the net on WebMD or About.com on breast discharge.