HER2 exon 20 insertion mutations and myelosuppression in lung adenocarcinoma patient: a case report and response to trastuzumab deruxtecan

BACKGROUND: Human epidermal growth factor receptor 2 (HER2) mutations occur in 2% of lung cancers. CASE PRESENTATION: In this report, we presented a case of an Asian female who was diagnosed with lung adenocarcinoma. NGS results indicated HER2 exon 20 insertion mutation and PET/CT results showed multiple metastases in lower lobes of both lungs. Thereafter, she was treated with chemotherapy alone, combination of chemotherapy and targeted therapy and immunotherapy. Due to progressive disease, she was then received DS-8201. Imaging data indicated partial response to DS-8201 and tumor marker values decreased significantly, suggesting good efficacy. Nevertheless, DS-8201 was discontinued because of the development of myelosuppression (grade 3). Finally, she died at home due to platelet deficiency, white blood cell (grade 4), granulocytopenia, intracranial hemorrhage and gastrointestinal hemorrhage. CONCLUSIONS: This was an important case since it exerted effective response to DS-8201. Meanwhile, myelosuppression is also found in the patient, which requires attention to pulmonary symptoms and careful monitoring.