Immune Checkpoint Inhibitors for Solid Tumors in the Adjuvant Setting: Current Progress, Future Directions, and Role in Transplant Oncology

Simple Summary Immune checkpoint inhibitors (ICIs) are being increasingly used after primary treatment of early-stage tumors to treat any residual disease and prevent recurrence. Herein, we provide a comprehensive review of pivotal clinical studies demonstrating efficacy and safety outcomes when ICIs are utilized after surgery in patients with melanoma, urothelial cancer, renal cell carcinoma, lung cancer, gastroesophageal cancer, and hepatobiliary malignancies. In addition, we highlight the potential role of these agents within the emerging field of transplant oncology. To guide the selection of eligible patients for ICIs, we outline approved and emerging biomarkers that may predict benefit from use of these agents and help monitor response, especially in the absence of visible disease on imaging. Furthermore, we provide real-world considerations with regards to tolerability and cost-effectiveness of these agents and necessary future directions that should be explored to increase the survival outcomes associated with the use of ICIs after surgery. The rationale for administering immune checkpoint inhibitors (ICIs) in the adjuvant setting is to eradicate micro-metastases and, ultimately, prolong survival. Thus far, clinical trials have demonstrated that 1-year adjuvant courses of ICIs reduce the risk of recurrence in melanoma, urothelial cancer, renal cell carcinoma, non-small cell lung cancer, and esophageal and gastroesophageal junction cancers. Overall survival benefit has been shown in melanoma while survival data are still not mature in other malignancies. Emerging data also show the feasibility of utilizing ICIs in the peri-transplant setting for hepatobiliary malignancies. While ICIs are generally well-tolerated, the development of chronic immune-related adverse events, typically endocrinopathies or neurotoxicities, as well as delayed immune-related adverse events, warrants further scrutiny regarding the optimal duration of adjuvant therapy and requires a thorough risk-benefit determination. The advent of blood-based, dynamic biomarkers such as circulating tumor DNA (ctDNA) can help detect minimal residual disease and identify the subset of patients who would likely benefit from adjuvant treatment. In addition, the characterization of tumor-infiltrating lymphocytes, neutrophil-to-lymphocyte ratio, and ctDNA-adjusted blood tumor mutation burden (bTMB) has also shown promise in predicting response to immunotherapy. Until additional, prospective studies delineate the magnitude of overall survival benefit and validate the use of predictive biomarkers, a tailored, patient-centered approach to adjuvant ICIs that includes extensive patient counseling on potentially irreversible adverse effects should be routinely incorporated into clinical practice.