As another example obviously supporting Warburg's hypothesis, low levels of cytochrome c oxidase (COX) were shown in a colon cancer cell line and postulated to be caused by impaired function of p53 in these cells, since p53 seems to be a necessary factor for the expression of an essential assembly factor for COX, SCO2 [15]. This evidence concerns the gene TP53 and malignant colon neoplasm.