RESUMEN
BACKGROUND: To date, lactate dehydrogenase (LDH) and S100B remain the most useful biomarkers for follow-up of melanoma patients. In recent years, indoleamine 2,3-dioxygenase (IDO), an immunosuppressive enzyme, has been proposed as a new potential tumour biomarker for melanoma. However, further studies are needed to confirm the usefulness of IDO expression as an independent prognostic factor. OBJECTIVE: To explore the potential association between serum IDO levels and melanoma stage at diagnosis and recurrence, and to compare the results to those obtained with LDH and S100B. In addition, we also investigated a possible cut off for IDO level as a prognostic factor for overall survival. METHODS: IDO, LDH and S100B levels were measured in serum samples of 186 patients in all melanoma stages at diagnosis and twice a year thereafter. A cut-off point for IDO levels was calculated using receiver operating characteristic curves to explore the association between these levels and the likelihood of lymphatic spread. Survival curves were estimated for patient groups stratified by IDO level (higher or lower than the cut off), using the Kaplan-Meier method. RESULTS: At diagnosis, serum IDO levels were significantly higher in stages IB, II, III and IV, whereas S100B levels were significantly higher in stages III and IV, and LDH levels were only higher in stage IV. In relapsed patients, significant increases were found in levels of all three markers. Finally, overall survival was significantly longer in patients with IDO levels below a cut off of 1.65 µM at diagnosis than in those with higher levels (91.3 vs. 71.0% at 36 months). CONCLUSION: In melanoma patients, serum IDO levels are significantly associated with disease stage, relapses and overall survival. These results indicate IDO could be a useful serum prognostic marker for melanoma.