A new report* (links to abstract) from Jessica Hawes and Karlyne Reilly at the National Cancer Institute describes a new genetically engineered mouse model of NF1 in which the tumors literally become illuminated. This is thanks to a luciferase reporter gene that ‘lights up’ a cell whenever and wherever tumor cells are growing. ‘Glowing’ cells can be detected through bioluminescence imaging of the living animal. This system can be used to identify tumors at different stages and to understand how and where spontaneous NF1 tumors initiate. The new mouse model will have tremendous value in screening candidate tumor drugs.