My sister drives me crazy saying that if anyone hits her breasts to hard (or bumps into them) she will get breast cancer. I told her this is not true but I just wanted to prove to her by seeing other people's answers. Thanks for the help.

You are right.

no, breast cancer is not caused by physical injury or trauma.

Breast cancer, like all other cancers, happens when normal cells change so that they grow in an uncontrolled way. This uncontrolled growth causes a tumour to form. No blow to the breast, or any punch, pinch etc can trigger this process.

Here is a link to an article about breast cancer myths, including this one

http://www.netwellness.org/question.cfm/… (first paragraph)

this should not cause it
everyone gets theres bumped alot

that is just a myth.