Immunotherapy, including immune checkpoint inhibitor (ICI) therapy, has been a paradigm shift in cancer therapeutics, producing durable cancer responses across a range of primary malignancies. ICI drugs increase immune activity against tumor cells, but may also reduce immune tolerance to self-antigens, resulting in immune-mediated tissue damage. ICI-associated hepatotoxicity usually manifests as hepatocellular enzyme elevation and may occur in 2%–25% of ICI-treated patients. Although ICI-associated hepatotoxicity is clinically and pathologically distinct from idiopathic autoimmune hepatitis, our understanding of its pathogenesis continues to evolve. Pending greater understanding of the pathophysiology, mainstay of management remains through treatment with high-dose corticosteroids. This approach works for many patients, but up to 30% of patients with high-grade hepatotoxicity may not respond to corticosteroids alone. Furthermore, atypical cholestatic presentations are increasingly recognized, and rare cases of fulminant hepatitis due to ICI hepatotoxicity have been reported. Optimal management for these challenging patients remains uncertain. Herein, we review the current understanding of pathogenesis of ICI-associated toxicities, with a focus on hepatotoxicity. Based on the existing literature, we propose evolving management approaches to incorporate strategies to limit excess corticosteroid exposure, and address rare but important presentations of cholestatic hepatitis and fulminant liver failure. Finally, as ICI hepatotoxicity frequently occurs in the context of treatment for advanced malignancy, we review the impact of hepatotoxicity and its treatment on cancer outcomes, and the overall safety of re-challenge with ICI, for patients who may have limited treatment options.

Background and aims: Immune checkpoint inhibitors (ICI) are increasingly used in cancer therapy. Elevated liver enzymes frequently occur in patients treated with ICI but evaluation is poorly described. We sought to better understand causes of liver enzyme elevation, investigation and management. Methods: Patients treated with anti-PD-1, PDL-1 or CTLA-4 therapy in Phase I/II clinical trials between August 2012 and December 2018 were included. Clinical records of patients with significant liver enzyme elevations were retrospectively reviewed. Results: Of 470 ICI-treated patients, liver enzyme elevation occurred in 102 (21.6%), attributed to disease progression (56; 54.9%), other drugs/toxins (7; 6.9%), other causes (22; 21.6%) and ICI immunotoxicity (17; 16.7%; 3.6% of total cohort). Immunotoxicity was associated with higher peak ALT than other causes of enzyme elevation (N = 17; M = 217, 95% CI 145–324 for immunotoxicity, N = 103; M = 74, 95% CI 59–92 for other causes; ratio of means 0.34, 95% CI 0.19–0.60, p = <0.001) and higher ALT:AST ratio (M = 1.27, 95% CI 0.78–2.06 for immunotoxicity, M = 0.69, 95% CI 0.59–0.80 for other causes, ratio of means 0.54, 95% CI 0.36–0.82, p = 0.004). Immunotoxicity was more often seen in patients with prior CPI exposure (41.2% of immunotoxicity vs 15.9% of patients without, p = 0.01), anti-CTLA-4 –containing ICI treatments (29.4% of immunotoxicity vs 6.8% of patients without, p = <0.001) and other organ immunotoxicity (76.5% of immunotoxicity vs 19.2% of patients without, p = <0.001). Cause for enzyme elevation was established in most patients after non-invasive investigation. Liver biopsy was reserved for four patients with atypical treatment response. Conclusions: Liver enzyme elevation is common in patients receiving ICI, but often has a cause other than immunotoxicity. A biochemical signature with higher ALT and ALT/AST ratio, a history of prior ICI exposure and other organ immunotoxicities may help to identify patients at a higher likelihood of immunotoxicity. Liver biopsy can be safely deferred in most patients. We propose an approach to diagnostic evaluation in patients with liver enzyme elevations following ICI exposure.

Chronic hepatitis C infection represents a significant and growing health problem worldwide. Patients with genotype 1 hepatitis C respond poorly to the current standard of care, pegylated interferon and ribavirin, which is frequently associated with unpleasant side effects. Consequently new agents with improved efficacy and tolerability are needed. The efficacy and safety of the direct-acting antiviral agent telaprevir in the treatment of genotype 1 hepatitis C infection have been demonstrated in a number of clinical trials. The addition of telaprevir to standard therapy considerably improves response rates and allows response-guided shortening of treatment duration in a substantial number of treatment-naïve patients. Side effects associated with telaprevir therapy include rash, anaemia, gastrointestinal disturbance and anorectal discomfort. Telaprevir-resistant variants have been identified in patients who have failed telaprevir-containing therapy, and whether selection of these variants will compromise future therapeutic options is currently unknown. The efficacy and safety of telaprevir in the treatment of the most challenging patients, including those with recurrent hepatitis C following liver transplantation and those co-infected with HIV, remains to be established.

Endothelin‐1 is a potent vasoconstrictor and a therapeutic target in pulmonary arterial hypertension. Endothelial cells are the physiological source of endothelin‐1 but in vitro data from our group shows that interferons (IFNα, IFNβ or IFNγ) induce endothelin‐1 in pulmonary vascular smooth muscle cells. IFNs are integral to innate immunity and their antiviral and immunomodulatory capability has been harnessed therapeutically; for example, IFNα plays a critical role in the treatment of chronic hepatitis C infection. However, in some patients, IFN causes pneumonitis and possibly irreversible pulmonary arterial hypertension. In this study, we found that of 16 patients undergoing a six‐month course of IFNα therapy, two demonstrated considerably increased serum levels of endothelin‐1. We propose that IFN therapy results in elevated levels of endothelin‐1 in some patients and when clinically significant levels are reached, pulmonary side effects could ensue. This hypothesis can be easily tested in IFN‐treated patients by measuring serum endothelin‐1 levels and cardiopulmonary physiological parameters.