One of the biggest challenges in cancer treatment is choosing the right regimen for a given patient. Treatment strategies work differently for different tumors. In choosing effective treatments with minimal side effects, oncologists rely heavily on biopsy reports that diagnose the tumor type involved. However, even today, cancer diagnosis is done the old-fashioned way: by observing morphological changes in biopsies under the microscope. The method suffers from serious limitations because cancer cells that look similar under the microscope can follow different clinical courses and respond differently to therapy. Now, in a new study reported in Friday's Science,a team of Whitehead-led researchers reports the first systematic and objective approach for identifying and classifying tumor types.