Still these promoted cells do not multiply uncontrollably unless something else happens to them. Very few things have the ability to initiate cancer and promote it and make it progress. In any case, you can compare cancer to a rope hanging from a tree branch. If the rope is cut, then you have a cancer. You can think of carcinogens as bullets being fired at the rope.
Most bullets miss the rope completely.
A few hit the rope and damage it. As time passes and more and more carcinogens are fired at the rope, eventually the rope may be cut and cancer develops. This is the truth about cancer, including breast cancer. The same rate of increase is visible in Canada, Japan, Denmark, the Nordic countries, and elsewhere in the 'developed' world. The reasons for this steady increase are not understood.