The luciferase gene or luciferase bioluminescence does not affect the growth of tumors in mice. B16-F10 cells (1 × 106) expressing GFP alone or GFP-P2A-luc (clone 4) were injected subcutaneously into the right or left flank respectively of white C57Bl/6 mice. Mice received bi-weekly injections of either PBS or D-luciferin (150 mg/kg) and tumor growth was recorded using calipers for GFP alone (A) or GFP-P2A-luc (B). Ellipsoid volume was determined using the formula π/6 × (L × W)3/2 . After 21 days, bioluminescent imaging was performed on tumors expressing GFP-P2A-luc (C) using the Xenogen IVIS-100. (D) Images were analyzed using Living Image software and represented as total flux measurements in photons/second. (E) Weight data was recorded from the excised tumors at sacrifice day 21. Statistical significance was assessed using non-parametric (Mann-Whitney) analysis using GraphPad Prism 5.01. Data is the mean ± s.e.m. from 4 independent experiments.