(University of Texas M. D. Anderson Cancer Center) Researchers at The University of Texas M. D. Anderson Cancer Center have discovered that when treated with Herceptin prior to surgery, 50 percent of HER2 positive, breast cancer patients showed no signs of disease at the time of surgery.

However, of those women who had residual disease, about one-third had tumors that converted from HER2 positive to HER 2 negative status -- possibly indicating a resistance to the targeted therapy.