Targeting Angiogenesis in the Era of Biliary Tract Cancer Immunotherapy: Biological Rationale, Clinical Implications, and Future Research Avenues

Simple Summary The incidence of biliary tract cancers (BTCs) is rising. Although therapeutic weapons are still limited, a better knowledge of the molecular landscape of these tumors has established the conditions for several phase I and II clinical trials in which molecular targeted drugs are combined with chemotherapy. Clinical research is investing great efforts in immunotherapy, which has recently transformed the treatment of many cancers. In BTCs, the efficacy of immunotherapy is limited by the high percentage of patients presenting immunosuppressive features in the tumor microenvironment. Angiogenesis is known to play a key role in modulating the microenvironment by excluding cytotoxic immune cells from the tumor bed, favoring an immunosuppressive activity. Therefore, blocking angiogenesis could create the conditions for more efficacious immunotherapy. This review considers clinical trials based on therapy combining angiogenesis and immune cell inhibitors, highlighting the clinical need for phase III studies in a precision-medicine era. Although biliary tract cancers are traditionally considered rare in Western countries, their incidence and mortality rates are rising worldwide. A better knowledge of the genomic landscape of these tumor types has broadened the number of molecular targeted therapies, including angiogenesis inhibitors. The role of immune checkpoint inhibitors (ICIs) could potentially change the first-line therapeutic approach, but monotherapy with ICIs has shown disappointing results in CCA. Several clinical trials are evaluating combination strategies that include immunotherapy together with other anticancer agents with a synergistic activity. The tumor microenvironment (TME) composition plays a pivotal role in the prognosis of BTC patients. The accumulation of immunosuppressive cell types, such as tumor-associated macrophages (TAMs) and regulatory T-cells, together with the poor infiltration of cytotoxic CD8+ T-cells, is known to predispose to a poor prognosis owing to the establishment of resistance mechanisms. Likewise, angiogenesis is recognized as a major player in modulating the TME in an immunosuppressive manner. This is the mechanistic rationale for combination treatment schemes blocking both immunity and angiogenesis. In this scenario, this review aims to provide an overview of the most recent completed or ongoing clinical trials combining immunotherapy and angiogenesis inhibitors with/without a chemotherapy backbone.