Stochastic bioluminescence correlates with spontaneous tumorigenesis. (A) Summary of physical examination and bioluminescent imaging data from 10 spontaneous lesions that developed in a cohort of TAX-LUC animals over the period of 1 year. (B) Frequency with which bioluminescence is associated with various stages in tumor development. (C) Frequency of bioluminescence within the cohort over time increases as animals develop spontaneous tumors.