HYI and neoplasm: Three hypotheses arise: (i) an alteration of the glyoxalate metabolism in CRC cells; (ii) an enhancement of the metabolic flux to serine synthesis necessary to obtain glycine, glutathione, NADPH, and nucleotides, suggesting probable tumor-promoting effects as consequences of the putative lost Hyi activity; (iii) a probable action of putative Hyi as a tumor-suppressor of CRC that is inhibited by cancerous cells specifically in the superficial region of the tumor (Figure 6a).