Jan. 26, 2009 -- When a woman has a mastectomy to remove breast cancer in one breast, what should she do about the other breast?

Her first breast cancer may hold some clues, according to a new study, published in the advance online edition of Cancer.

"Not every woman who has breast cancer will get another breast cancer in the opposite breast," researcher Kelly Hunt, MD, tells WebMD.

"We tried to distill down some of those factors with our study and figure out which ones may be the most important ones," says Hunt, a professor of surgical oncology at the University of Texas M.D. Anderson Cancer Center.

But the findings don't amount to a checklist for getting a preventive mastectomy; breast cancer experts say that's still a personal decision that each patient must weigh with her doctors.