Characterization of mitochondrial status and oxidative stress levels with the increasing age of multicellular spheroids, coupled with enhanced glycolysis and related variations in HIF-1α and c-Myc will prove useful in optimizing the use of this valuable cellular 3-D tumor model for predicting tumor response to chemotherapeutic/radiosensitizing agents acting on metabolic pathways. This evidence concerns the gene HIF1A and neoplasm.