FFAR4 and cancer: Among them, acetic acid level is lower and hexadecanoic acid/octadecanoic acid is higher in cancer patients than in healthy controls (13).The free fatty acid receptor (FFAR) family is comprised of FFAR1–4, formerly known as GPR40, GPR43, GPR41, and GPR120, respectively; FFAR1 and FFAR4 are both receptors for LCFAs, and FFAR2 and FFAR3 are both receptors for SCFA (14–16).