[Indoleamine 2,3-Dioxygenase Activity during Fulvestrant Therapy for Multiple Metastatic Breast Cancer Patients]

We evaluated the clinical significance of indoleamine 2,3-dioxygenase(IDO)during fulvestrant therapyfor multiple metastatic breast cancer patients. IDO activitycan be measured using the tryptophan(Trp)/kynurenine(Kyn)ratio. Trp and Kyn were measured using high-performance liquid chromatography(HPLC). The serum Trp/Kyn level in patients with multiple metastatic breast cancer was lower than in patients without metastases. IDO activityincreased after breast cancer metastases developed. IDO activitywas correlated with the number of metastatic lesions during toremifene and fulvestrant therapy. These results suggested that measurement of the Trp/Kyn ratio is useful to evaluate immunological metastatic status during endocrine therapy.