The 35-year-old man has only just recovered from an operation in which the doctors removed his bladder tumor. A few months later he gets sick again: another tumor in his bladder. To make matters worse, the cancer cells have spread in his body and are relentlessly multiply- ing. The disease can be attributed to his mutated histiocytes – cells of the immune system that normally defend the body against invading germs. The doctors discover that there are two mutations in the cancer cells, including the muta- tion BRAFF595L , about which there is still only little research. Which of the two is causing the tumor to grow, and what is an appropriate thera- py to halt the progress of the disease? To find out, the doctors turn to the Freiburg biologist Dr. Tilman Brummer. He studies the signaling in cells and determines what processes cause a tu- mor to appear and spread – for instance due to BRAF mutations. Not Always the Same Pattern Brummer and his team are searching for sub- stances for targeted therapies that can take action at the right points on disrupted signaling paths. When a gene in a cell is mutated, the pro- teins developed according to its blueprint also change. “We’re testing whether and how already existing substances interact with the modified proteins,” explains Brummer. Cancer does not always follow the same pattern: A substance that halts the growth of a tumor in cells with one mutation can accelerate its development in other cancer cells. The researchers thus gather as much information as possible about a tumor to Scientists are developing targeted therapies to act on disrupted signaling networks and fight cancer The Tumor’s Weak Spot by Katrin Albaum 8