Response to Pyrotinib in a Chinese Patient with Bone-Metastatic Scrotal Paget’s Disease Harboring Triple Uncommon HER2 Mutation: A Case Report

BACKGROUND: Previous studies have suggested the efficacy of HER2 antibody (trastuzumab) in scrotal Paget’s disease with HER2 amplification or overexpression. However, no report about the effectiveness of HER2 inhibitor (pyrotinib) in those patients has been provided until now. CASE PRESENTATION: We present a case of a Chinese patient with bone-metastatic scrotal Paget’s disease harboring triple uncommon HER2 mutations (R678Q/S310Y/S310F). Due to poor conditions (severe anemia, thrombocytopenia, ECOG PS3), this patient could not tolerate traditional chemotherapy and radiotherapy. Then, the patient participated in a registered clinical trial (NCT03239015) about basket trial for intractable cancer. The patient received pyrotinib (400 mg po qd) and achieved a partial response for 4.0 months. CONCLUSION: This is the first report describing a patient with scrotal Paget’s disease harboring triple uncommon HER2 mutation who responds well to pyrotinib. This case suggested that HER2 mutation is also a potential biomarker for treatment in extramammary Paget’s disease and pyrotinib may be an ideal choice for these patients.