A Case of Solitary Brain Metastasis Two Years after Resection of HER2-Positive Advanced Gastric Cancer

A 75-year-old man underwent laparoscopic total gastrectomy for advanced gastric cancer in 2020. Pathological diagnosis showed lymphatic invasion at the oral margin and the gastrectomy was considered a non-curative resection. Immunostaining showed HER2[3+] and the patient received 8 courses of trastuzumab+capecitabine+cisplatin and 16 courses of capecitabine monotherapy as adjuvant chemotherapy. About 2 years after surgery, the patient was referred to a local hospital due to weakness in the left lower limb and a fall. A CT scan revealed a metastatic brain tumor. When he was transferred to our hospital, there was no other metastasis. The patient then underwent craniotomy at the Department of Neurosurgery. Postoperative pathology determined that the tumor was a metastatic tumor of gastric cancer. The patient had a single intracranial recurrence after trastuzumab administration. Therefore, we administered nivolumab to prevent systemic recurrence including additional intracranial metastasis. The patient has been recurrence-free for 6 months after craniotomy. In this report, we describe a case of a patient with a solitary brain metastasis after anti-HER2 therapy following resection of HER2-positive advanced gastric cancer.