D-Luciferin is a popular bioluminescent substrate of luciferase in the presence of ATP, used in luciferase-based bioluminescence imaging and cell-based high-throughput screening applications. In an immunocompetent mouse model of ovarian cancer, the use of D-luciferin substrate and firefly luciferase preserves tumour-host immune interactions since bioluminescent imaging is a more sensitive indication of tumour growth than weight gain.