IDO2 and medullary thyroid gland carcinoma: Moreover, in the log-rank test, no significant difference in RFS was observed in the male MTC patients according to the IDO2 expression (P = 0.397; Fig. 2D), whereas the IDO2-low group showed a better prognosis than the IDO2-high group in female MTC patients (P = 0.016; Fig. 2 F).