Harvard researchers working at Massachusetts General Hospital’s Radiation Oncology unit have used a powerful new microscope to see inside cancerous tumors. The microscope is so powerful that it can see individual cells within a tumor. “We can see what’s going on under the surface of the tumor without disturbing the tumor itself,” says principal investigator Rakesh Jain, the A. Werk Cook Professor of Radiation Oncology in the Harvard-MIT Division of Health Sciences and Technology. “This new technology gives us the ability to look deep inside the tissues of animals,” says Edward Brown, a post-doctoral fellow in Jain’s lab. The scientists are using a technique called multiphoton laser scanning microscopy to visualize individual cells. This technology allows them to monitor gene expression, therapy effectiveness and interactions between tumor cells and normal cells.