Figure 5.

Metabolic compartmentalization of mitochondrial activity in skeletal muscle and human breast cancer. Frozen sections from skeletal muscle tissue or human breast cancers were subjected to a routine histochemical stain that detects the functional activity of mitochondrial complex IV [cytochrome C oxidase (COX)]. This allows the visualization of oxidative mitochondrial metabolism in tissue sections. COX-positive cells are positively stained brown (see red arrows). In skeletal muscle, note that fast-twitch fibers are glycolytic (Gly) and are COX-negative, while slow-twitch fibers are oxidative (Ox) and are COX-positive. In breast cancers, the tumor stroma is glycolytic (Gly) and is COX-negative, while epithelial tumor cell nests are oxidative (Ox) and are COX-positive. These results support the idea that tumors show metabolic compartmentalization and specialization, as occurs in skeletal muscle tissue. Reproduced and modified with permission from reference ¹⁴.