Objective  To investigate the value of amino acid metabolomics in evaluating chemotherapeutic response of patients with advanced breast cancer, the changes in the levels of 32 amino acids in the circulating serum of patients before(baseline)and after thefirst cycle(prognosis)of chemotherapy were tested.

  Methods  Seventy-three advanced breast cancer patients with local recurrenceand distant metastasis admitted at the Liaoning Cancer Hospital from March 2015 to October 2016 were enrolled.Peripheral bloodsamples(2 mL)were collected before and after the first cycles of chemotherapy from each patient.Thirty-two amino acids in the serum were tested using the ultra-performance liquid chromatography-tandem mass spectrometry(LC-MS/MS).Patients were categorized into the improvement or deterioration groups, based on the first imaging test after 2-4 cycles of chemotherapy.The changes inamino acids levels were analyzed in different prognosis groups.

  Results  The levels of the 32 amino acids ranged 3-180000 pmol/L.Compared to their baseline levels, both glycine and L-glutamine increased in the improvement group, but decreased in the deterioration group.Sarcosine was significantly reduced in the improvement group, while differences in its levels were not obvious in the deterioration group.L-threonine, taurine, iminodiacetic acid, and L-glutamic acid were increased in both groups.

  Conclusion  Changes in theserum levels of glycine, sarcosine, and the other amino acids before and after the first cycles of chemotherapy can predict chemotherapeutic response in patients with advanced breast cancer.Amino acid metabolomics may become a potential biomarker for predictingthe efficacy of chemotherapy earlier than that of imaging tests, and thereby help improve therapeutic strategies for advanced breastcancer.