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Suyao Li,1,* Qing Liu,1,2,* Mengling Liu,1 Tianshu Liu1,2 1Department of Medical Oncology, Zhongshan Hospital, Fudan University, Shanghai, People’s Republic of China; 2Cancer Center, Zhongshan Hospital, Fudan University, Shanghai, People’s Republic of China*These authors contributed equally to this workCorrespondence: Tianshu Liu, Department of Medical Oncology, Zhongshan Hospital, Fudan University, No. 180 Fenglin Road, Shanghai, 20032, People’s Republic of China, Email liutianshu1969@126.comBackground: The highest incidence of human epidermal growth factor receptor 2 (HER2) mutations has been observed in bladder cancer (BC). However, the function of HER2 mutation in tumor progression and metastasis remains unclear. Currently, no responses to the pan-HER kinase inhibitor were observed in HER2-mutant BC.Case Presentation: We described a patient with metastatic bladder urothelial carcinoma (BUC) carrying a HER2 V842I mutation both in circulating tumor DNA (ctDNA) and biopsy sample. The patient was then treated with a HER2 tyrosine kinase inhibitor, pyrotinib, and responded well. However, the targeting treatment was terminated due to G3 diarrhea. Reduced dose of pyrotinib was later added to late-line treatment, the patient’s tumor again responded with a significant decrease in CA199.Conclusion: This is the first reported case of HER2 V842I mutation successfully treated with pyrotinib in BUC, suggesting pyrotinib therapy might serve as a therapeutic option for BUC patients harboring HER2 activating mutation.Keywords: bladder cancer, pyrotinib, V842I mutation, human epidermal growth factor receptor 2, next-generation sequencing