Efficacy of trastuzumab deruxtecan in an advanced gastric cancer patient with brain metastasis

Background: There is no clinical evidence supporting the effectiveness of trastuzumab deruxtecan (T-DXd) for treating advanced gastric cancer (AGC) with brain metastasis. Case report: This is a case of a 65-year-old man with human epidermal growth factor-2 (HER2)-positive AGC. He was initially treated with capecitabine, cisplatin, and trastuzumab, followed by paclitaxel and ramucirumab, nivolumab, trifluridine and tipiracil, and irinotecan regimens in addition to radiation therapy for brain metastasis. The patient exhibited refractoriness to the standard regimen used for AGC and developed relapse of the brain metastasis after radiation accompanied by headache, nausea, and dizziness. In August 2020, following the approval of T-DXd for HER2-positive AGC, he received T-DXd therapy. After 5 cycles of T-DXd, contrast-enhanced computed tomography and magnetic resonance imaging demonstrated significant tumor shrinkage and improvement of symptoms. Conclusion: T-DXd demonstrated effectiveness for the treatment of brain metastasis arising from HER2-positive AGC.