See below. Keep current on mammography. Stop smoking, maintain an ideal body weight. Depending on how strong your family history is, and if you have a proven genetic mutation, you could be a candidate for prophylactic mastectomy, with or without removal of the ovaries. Visit with a medical oncologist to find out your options.
Prevention. Implies "fixing the underlying defect" and this sort of genetic engineering has not arrived - vectoring the gene in may not lead to its propoer regulation (turning on and off properly for instance). Early detection--proper cost effective screening, or avoidance of co-factors for induction seem resaonable choics.