1. Department of Oncology, Istituto di Ricerche di Biologia Molecolare, Merck Research Laboratories, 00040 Rome, Italy.
2. Department of Applied Computer Science and Mathematics, Merck Research Laboratories, Rahway, 07065-0900, NJ.
3. Department of Comparative Medicine and Laboratory Animal Resource, Istituto di Ricerche di Biologia Molecolare, Merck Research Laboratories, 00040 Rome, Italy.
4. Department of Clinical and Biological Sciences, University of Turin, 10100 Turin, Italy.