HDAC4 and cancer: For example, D-erythrose 4-phosphate, fructose 6-phosphate, D-ribose 5-phosphate, and D-sedoheptulose 7-phosphate, which belong to PPP, were highly negatively correlated with transcript levels of HDAC4. PPP is one of the fundamental components of cellular carbohydrate metabolism and is especially crucial for cancer cells (Kowalik et al., 2017).