Myocarditis in a patient treated with Nivolumab and PROSTVAC: a case report

Immune checkpoint inhibitors have revolutionized treatment and improved survival in many cancers. However, since immune-related adverse events (irAEs) are potentially fatal, early recognition and prompt treatment are warranted. One of the rarest but most dramatic irAE is myocarditis, which has significant morbidity and mortality if not recognized and treated early. To report the first case of myocarditis in a patient with metastatic castration-resistant prostate cancer (mCRPC) treated with a combination of nivolumab, an anti-programmed cell death protein 1 antibody, and PROSTVAC, a vector-based therapeutic prostate cancer vaccine. A 79-year-old man with mCRPC metastatic to bone and lymph nodes and a history of atrial fibrillation presented with blurred vision and pain and stiffness in the upper back after 8 weeks on a clinical trial with nivolumab (1 mg/kg) and PROSTVAC, both given every 2 weeks. Eye exam was within normal limits, while musculoskeletal exam revealed tenderness in trapezius muscles and decreased motor strength in arms (III/V) and neck (IV/V). The rest of the physical exam was within normal limits, with the exception of an irregular heart rhythm. Laboratory tests were as follows: creatinine kinase (CK) 3200 U/L (normal: 39-308 U/L), CK-MB 65.7 mcg/L (normal: 0-7.6 mcg/L), troponin I 0.209 ng/mL (normal: 0-0.056 ng/mL). Electrocardiogram (ECG) revealed atrial fibrillation with QT prolongation (QTc 514 msec) and left anterior fascicular block, unchanged from baseline. 2D-echocardiogram showed a left ventricular ejection fraction of 65% with an enlarged left atrium, dilated right ventricle, and increased pulmonary artery pressure (45 mmHg). ProBNP was elevated at 1463 pg/mL and peaked at 3066 pg/mL one day after hydration. With a presumed diagnosis of autoimmune myositis and possible myocarditis, the patient was admitted and started on methylprednisolone 1 mg/kg/day. Cardiac MRI showed elevated native myocardial T1 values consistent with myocarditis (Fig. 1). The patient was discharged on a prednisone taper after normalization of cardiac enzymes on day 4. Treatment with PROSTVAC continued for three more months; nivolumab was discontinued. Six months later, patient is doing well, with no residual cardiac damage. Cardiovascular irAEs are relatively rare (< 1%) and have a variety of clinical presentations. Myocarditis is potentially life-threatening and can range from subclinical to fulminant. Therefore, clinical suspicion, early detection, and pr