BACKGROUND The pathogenesis of breast cancer remains unclear. AIMS To investigate the pathogenesis of breast cancer through targeted metabolomics of amino acids components in serum of patients with breast cancer. METHODS Patients with breast cancers were enrolled in our hospital between year January 1(st), 2013 and December 31(st), 2014. Targeted analysis of amino acids was performed using ESI-QTOF-MS instrument. In vitro experiment was performed to determine the influence of tryptophan towards interleukin-10 (IL-10) secretion by CD4+ T cell. RESULTS Targeted metabolomics of amino acids showed that the level of tryptophan significantly (p<0.05) increased in patients with breast cancer. Furthermore, the biological function of tryptophan was determined through determining the influence of tryptophan towards IL-10 secretion using in vitro method. The addition of tryptophan (100 uM) in the cell medium can significantly inhibited the secretion of IL-10 by CD4+ T cells, as indicated by the mRNA level and protein concentration. CONCLUSION The inhibition of IL-10 secretion by CD4+ T cells is a potential pathogenesis of breast cancer.