A Case Report on the Efficacy of Trastuzumab Emtansine in a Patient With Human Epidermal Growth Factor Receptor 2 Exon 20-Mutated Adenocarcinoma of the Lung

Lung cancer is the foremost reason for cancer-related mortality among men and women. The ultimate goal of patient supervision post-diagnosis for advanced cases is to improve survival and quality of life with minimal treatment-associated side effects. With advancements in genomic medicine and a better understanding of cell signaling pathways, many actionable gene mutations have been identified in lung carcinoma, which drastically improve survival outcomes. Mutations in human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor together are observed in nearly 1-3% of cases and act as an oncogenic driver. In the case of HER2-mutant lung cancers, there are limited approved agents, and the treatment represents a critical unmet medical need because of the poorer survival outcomes compared to patients with additional oncogenic drivers. The recent standard of care of treatment is chemotherapy, but reports suggest that compared with cytotoxic chemotherapy, patients receiving HER2-directed therapies have relatively longer median survival duration. Here, we report a case of HER2 exon 20-mutated metastatic lung adenocarcinoma patient who received trastuzumab emtansine in the third-line setting and achieved durable disease control.