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Chronic inflammatory arthritis following checkpoint inhibitor therapy for cancer: game changing implications

The use of immune checkpoint inhibitor (ICI) therapy for cancer is now a pillar of oncological therapeutics and growing, with an estimated 43.5% of all tumours falling within current labelling indications for use.1 Eventually as the accessibility to ICI therapy increases, these data have staggering implications, given that an estimated number of new cancers in Europe and the USA exceeds 5 million individuals yearly.2 As a byproduct of this tidal wave of newly exposed patients to various forms of immunotherapy with estimates that 10%–20% or more who may develop serious immune related adverse events (irAEs),3 it is inevitable that the evaluation and care of such patients will pose a challenge to existing healthcare systems and likely create a space for a new specialty to manage such. From a rheumatological perspective, let us now consider that an estimated 3%–7% of ICI exposed patients may develop inflammatory arthritis (IA),4 5 making it seem inevitable that ICI associated IA will become ever more commonplace, giving us pause to ask ourselves what our current understanding of this disorder is and how prepared we are to manage it.

These irAEs are heterogeneous and appear to differ in their presentations, similarity to existing constructs of autoimmune diseases and their natural history. To help focus the discussion regarding these complications and based on the available data on IrAEs, we propose a classification of them into three main categories (box 1). Most irAEs are self-limiting in nature and while they may have lasting clinical effects such as ongoing requirement for hormone replacement therapy in some endocrinopathies, the inflammatory phase of these illnesses is largely self-limiting with few exceptions, with less than 10% requiring additional therapy after suppression with glucocorticoids.6 A second category is the development of a classical autoimmune disease in subjects who were …