We describe four patients with non-small cell lung cancer who developed myositis after beginning treatment with osimertinib. In addition, we review the literature on osimertinib-associated myositis. Using PubMed, the following terms were searched and relevant citations assessed: creatine phosphokinase, myositis, osimertinib, rhabdomyolysis, osimertinib, and Tagrisso.
Thirty-eight patients were treated with osimertinib in our community clinic. Four with non-small cell lung cancer developed myositis after beginning treatment. The onset of symptoms and/or elevation of creatine phosphokinase occurred between two weeks and eleven months after osimertinib was initiated. Alternative causes for myositis were not identified. In two patients, myositis resolved within one month of withdrawing treatment. Two other patients continued osimertinib treatment with close monitoring.
Myositis is a serious and potentially underreported adverse effect of osimertinib. Previous studies suggest that osimertinib-associated myositis is rare, occurring in less than 1% of patients. However, myositis occurred in over 10% of patients treated with osimertinib in our clinic population. We suggest regular monitoring for myositis among patients being treated with osimertinib and dose-reduction or cessation of treatment if clinically indicated.