Cabozantinib-induced serum creatine kinase elevation and rhabdomyolysis: a retrospective study

BackgroundRhabdomyolysis is a potentially fatal disease, and elevated serum creatine kinase (CK) is one of the key laboratory findings suggestive of this disease. It is important to distinguish rhabdomyolysis from other diseases because CK elevation can occur in a variety of etiologies. Cabozantinib is one of the standard treatments for patients with renal cell carcinoma, but the frequency of CK elevation with this drug is still unknown.MethodsTo investigate the frequency of serum CK elevation induced by cabozantinib, we retrospectively reviewed the electronic medical records of patients with advanced renal cell carcinoma who received cabozantinib at our institution from April 2020 to March 2021.ResultsSeven patients were included in the study; six experienced serum CK elevation, four were classified as grade 1, and the remaining two as grade 3 according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. In five patients, the time from cabozantinib administration to CK elevation was 14 days. Hypothyroidism can be one of the causes of CK elevation; however, two patients who had hypothyroidism caused by previous treatment were in the euthyroid condition due to hormone replacement. One patient with grade 1 CK elevation developed late-onset immune-related adverse event (irAE) myositis comorbid with suspected myasthenia gravis. One patient with grade 3 CK elevation developed muscle weakness and rhabdomyolysis.ConclusionsCK elevation is a common adverse event induced by cabozantinib. Most patients are asymptomatic and may not be clinically ill. However, physicians should be careful with the rare occurrence of symptomatic serum CK elevation, indicating rhabdomyolysis and neuromuscular irAEs, especially in patients who receive immune checkpoint inhibitors (ICIs).