1. Department of Biology and Center for Cancer Research and
2. Merck & Co., Whitehouse Station, NJ 08889, USA.
3. Breast Center, Baylor College of Medicine, One Baylor Plaza, MS 600, Houston, TX 77030, USA.
4. Brigham and Women's Hospital, Department of Pathology, Boston, MA 02115, USA.
5. Department of Pathology, Tufts University Schools of Medicine and Veterinary Medicine, Boston, MA 02111, USA.
6. Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.