The battle to cure cancer, fought for three decades marked by failure and frustration, suddenly is in overdrive. Just a few weeks ago, reports rocked the medical world about two drugs that show promise in preventing breast cancer. This week, Wall Street and Main Street alike went wild over word of a bold experiment drug that wiped out tumors in mice. These developments underscore a much bigger story : A quiet revolution in genetics has brought scientists closer than ever before to finding an actual cure for cancer.