Tantalizing Clues to a Lethal Legacy

To most women, the notion of undergoing a mastectomy in order to prevent breast cancer smacks of wild paranoia. But for Maria Burkhardt of Covington, La., the unthinkable slowly became the inevitable. Twenty years ago, an aunt was stricken with the disease. Her mother died from it a decade later. In 1986 Maria's younger sister Jo Ann began fighting for her life. Next her older sister Rose developed an aggressive tumor. Maria consulted a doctor and was told she was "a ticking time bomb." Ominously, her tissues were judged too dense for mammograms to scan reliably.

So last summer, at 47,...