Display of representative biomolecular MALDI-MS images in (A) 2D and (B) 3D. PS(14:0/22:6) at m/z 818.4 and a tryptic peptide of hypoxia up-regulated protein (HYOU1) at m/z 1047.4, as well as LDHA at m/z 1071.5, colocalized with hypoxic regions, in which high levels of a tdTomato tryptic peptide at m/z 2225.0 were detected in MDA-MB-231-HRE-tdTomato breast tumor xenografts. This was evident in the 2D as well as the 3D display. The entire list of m/z values of hypoxia-up-regulated lipids and proteins, including all detected tryptic peptides per protein, is given in Tables S1 and S2, Supporting Information, respectively.