PRL and cancer: The metabolic pathways significantly altered in the positive ion mode include choline metabolism in cancer, glycerophospholipid metabolism, fatty acid degradation, riboflavin metabolism, pyrimidine metabolism, bile secretion, prolactin signaling pathway, galactose metabolism, glycolysis and gluconeogenesis, purine metabolism, and multiple amino acid metabolism pathways: for example, tryptophan, cysteine, methionine metabolism and valine, leucine, isoleucine biosynthesis.