Stefanie Raymond-Whish was 9 years old when her grandmother was diagnosed with breast cancer. A traditional Navajo who raised 15 children after her husband died in a car wreck, Raymond-Whish's ama' sa' ni seldom spoke about her illness. Even after her surgery, when she lived with the grandchildren and their mother, she always acted strong around the kids. It became a pattern: When Raymond-Whish was 13, her 38-year-old mother, Nellie Sandoval, was also diagnosed with breast cancer. And Sandoval was equally reserved on the subject. "My mother was really good about not appearing sick in front of us," says Raymond-Whish, now 32. "As a little girl, I knew about cancer, but didn't understand the impact of it at the time."

She understood it better by the time she was in college, in Flagstaff, Ariz., when a new tumor appeared in her mother's other breast. "When my mom had her recurrence, that's when it really hit me ... it was really upsetting. I went home to Farmington for her lumpectomy." Sandoval survived the disease, but not without a long struggle that included chemotherapy, radiation, and finally a double mastectomy. "My breasts were pretty mangled," says Sandoval, now 58. "So I said, 'Just get rid of them.' " Both Sandoval and her daughter have made breast cancer and its impact on Navajos the focus of their lives. Sandoval became an activist and filmmaker, working out of her papaya-colored home in Farmington, N.M. Raymond-Whish has taken her mission a step further: She works as a molecular biologist at the University of Northern Arizona, searching for breast cancer's root causes. "Is there any difference in how breast cancer develops in Native Americans and non-Native Americans?" she asks. One possible - and provocative - answer is emerging from her lab at the university: uranium.

Scientists have long known that uranium damages human cells. But in over six decades of atomic health testing, no one had ever noticed that uranium, at low doses, can act like an estrogen. No one, that is, until recently, when Raymond-Whish and her coworkers observed some unusual effects in lab animals.

Uranium can be found in several of the Jurassic sandstones that lie beneath the Four Corners region like a wrecked layered pastry. The target of frenzied mining throughout the Cold War, uranium ore has been wrenched from the ground, pulverized, milled and tossed in tailings across the Navajo Reservation. Low-level radioactive waste has dissolved into groundwater, escaped onto dust particles and blown off thousands of passing trucks to settle uneasily on surface soils. Over 1,000 abandoned uranium mines pockmark Navajo lands, but only half of them have been reclaimed. Exposure to uranium and its daughter elements has been linked to lung cancer, kidney damage and bone disease in Navajos, and it is the suspected culprit in numerous other medical conditions, from degenerative nerve disease and birth defects to a variety of other cancers.

Raymond-Whish's research lab is tucked inside a neo-Grecian edifice on the Northern Arizona University campus. With her gloved hands in a ventilated booth, the white-coated scientist carefully measures out uranium in solution into small test tubes. The solution will be injected into dishes of cultivated human breast cells, donated by a nun who died of breast cancer in 1979. The MCF-7 cells, as they are known, have been kept alive by the Michigan Cancer Fund through 178 generations of cell division. They are famous among researchers for the properties they exhibit in lab experiments. For example, estrogen causes them to proliferate rapidly - exactly as it does in real-life breast tissue, which is why many women diagnosed with breast cancer have their estrogen-producing ovaries removed. Raymond-Whish wants to see if the cells react in the same way to uranium.

"What I'm really interested in is the development of the mammary gland," says Raymond-Whish, who at this point is just weeks away from finishing her doctoral dissertation. A former teen rodeo star in barrel racing, she once wanted to be a veterinarian. But NAU didn't have a vet school, so she majored in zoology. That eventually landed her in the Discovery Research lab, where she studied the effects of pollution on tadpoles. She found she loved research. "It's like being a detective," she says.