Immune checkpoint inhibitor and tyrosine kinase inhibitor combinations have become the new standard of care in the first-line treatment of metastatic clear cell renal cell carcinoma. However, there is a growing concern regarding severe immune-related adverse events. A 78-year-old man with metastatic clear cell renal cell carcinoma, treated with pembrolizumab and axitinib, was admitted to the emergency department 30 days after initiating treatment due to rapidly progressive myositis. Myocarditis with severe ventricular dysfunction was identified. Muscular biopsy findings were compatible with inflammatory myopathy associated with immune checkpoint inhibitors. Initial treatment with high-dose corticosteroids showed an insufficient response. Therapeutic escalation on the third day with methylprednisolone, immunoglobulin, and abatacept resulted in clinical improvement. On the eleventh day, a sudden malignant arrhythmia occurred, followed by cardiac arrest. This represents one of the first case reports describing myocarditis and myositis during treatment with pembrolizumab-axitinib. While immune checkpoint inhibitor may play a major role, it is also possible that the tyrosine kinase inhibitor, while attempting to promote immune modulation, also increases severe toxicities.

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