Interestingly, 3D2-3, but not 3D1 stage MCTS or cells cultured in 2D, displayed expression of hypoxia-inducible factor 1α (HIF-1α) protein, typically detectable in hypoxic areas [32], similar to tumor xenografts generated in vivo upon s.c. injection of the same cells in immunodeficient animals (Figure 2E-2H and Supplementary Figure S2). The gene discussed is HIF1A; the disease is neoplasm.