Do you mean you can feel a bump or lump in your breast?
If so, see a doctor.
But if you mean can a physical bump/punch/thump to the breast cause cancer in later years - then no. Every woman will have had bumps to the breast area.
If you mean someone has bumped it, then I don't know. I did know a man who developed testicular cancer after receiving a hard impact in that area. Of course it could have been a coincidence. Either way, you should see your doctor straight away.
if you mean a lump, c ur gp. i went last week and mine was a cyst and sorted straighaway! they get u in really quick if you tell them you have a family history of breast cancer! should be within 2 weeks, mine was within 4 days! who says the nhs is crap!!