Univariate analysis identified IDO and PD-L1 expression (p = 0.02, Fig. 2b), surgical procedure (p = 0.01), final pathological stage (p = 0.003), lymph node metastasis (p < 0.001), and lymphatic invasion (p = 0.002) as significant prognostic factors for OS (Table 4). Here, IDO1 is linked to metastatic malignant neoplasm in the lymph nodes.