Combination therapies have been widely studied in recent years and offer a holistic approach to overcoming multiple obstacles within the tumor microenvironment, involving immune checkpoint inhibitors with other treatments like chemotherapy, radiotherapy, and targeted therapy, tumor vaccines, MEK inhibitors, CDK4/6 inhibitors, PARP inhibitors, IDO inhibitors, anti-angiogenic therapy and epigenetic therapy, which may overcome tumor immune escape and control metastases by enhancing or inducing new anti-tumor immune responses. Here, IDO1 is linked to neoplasm.