Abstract
Immune checkpoint inhibitor (ICI)-induced myocarditis is one of the most serious and potentially fatal toxicities of immunotherapy. Most of the guidelines for managing this toxicity are based on expert opinions. Human epidermal growth factor receptor 2 (HER2) alterations in non-small cell lung cancer (NSCLC) could be found using next-generation sequencing (NGS) on tissue and liquid biopsies. There is an approved first-line targeted therapy for HER2-positive breast and gastroesophageal cancers. Until now, no first-line targeted therapy for NSCLC with HER2 alterations has been approved. This case report presents a patient with metastatic HER2 NSCLC with a high PD-L1 level. She was started on first-line single-agent immunotherapy pembrolizumab. She tolerated the first two cycles well. Before the third cycle, she had palpitations and was tachycardiac. Furthermore, investigations found raised troponin levels. She was diagnosed with ICI-induced myocarditis. After being admitted to the cardiac care unit (CCU) and beginning pulse steroid treatment, she responded well with decreasing troponin levels.