HDAC9 and neoplasm: Propionic, butyric, and valeric acids are the most common microbiota-produced SCFAs that, as well established, exert positive metabolic effects on enterocytes, act as tumor suppressor agents, and regulate host gene expression via histone deacetylase inhibition (HDAC; Nankova et al., 2014; Yuille et al., 2018).