Growth factors are a type of organic compounds that are necessary for regulating the normal growth and metabolism of microorganisms, but cannot be synthesized using simple carbon and nitrogen sources. Broadly defined growth factors include not only vitamins, but also bases, purines, pyrimidines, biotins, and niacin, and sometimes amino acids required by amino acid deficient mutant strains; Narrowly defined growth factors generally only refer to vitamins. A class of peptide substances that regulate cell growth and other cellular functions through binding to specific, high affinity cell membrane receptors. It exists in platelets, various adult and embryonic tissues, and most cultured cells, and has certain specificity for different types of cells. Usually, the growth of cultured cells requires the coordinated action of multiple growth factor sequences, and tumor cells have the characteristic of independent growth factor independent and autonomous growth.