Immune Checkpoint Inhibitors as Switch or Continuation Maintenance Therapy in Solid Tumors: Rationale and Current State

First-line chemotherapy for many solid tumors is limited by toxicity. There is a growing interest in maintenance therapy as a strategy for prolonging the benefits of first-line therapy while minimizing toxicity. Maintenance therapy can comprise either continuation of an agent given as part of the first-line regimen (continuation maintenance) or treatment with a new agent (switch maintenance). Maintenance therapy is already established in several solid tumors, including lung, breast, gastric, colorectal, and ovarian cancer. Immune checkpoint inhibitor treatment has been shown to prolong duration of response and overall survival, but efficacy is generally restricted to a limited proportion of patients with selected tumors. Thus, efforts are ongoing to determine whether the clinical benefits of immune checkpoint inhibitors can be extended using novel treatment schedules and settings, including maintenance therapy. Early- and late-phase clinical trials have investigated the efficacy and safety of immune checkpoint inhibitors as switch and continuation maintenance in different tumors, and a range of phase III trials are ongoing. Interpretation of results requires consideration of trial designs, eligibility criteria, and primary endpoints, in addition to biomarker exploration, and assessment of quality of life and cost effectiveness. Findings from ongoing trials will help further define the role of immune checkpoint inhibitors as maintenance therapy across a spectrum of solid tumors.