Long-Term Complete Response to Trastuzumab Deruxtecan in a Case of Unresectable Gastric Cancer

Trastuzumab deruxtecan (T-Dxd) has been approved for the treatment of HER2-positive gastric cancer. However, there are only a limited number of cases of gastric cancer where a long-term complete response (CR) has been maintained. Consequently, we report a case of gastric cancer in which long-term CR was maintained.

A woman in her late 60s underwent a gastrointestinal endoscopy, which revealed a type 2 lesion with ulceration in the lesser curvature of the vestibule, and a biopsy, which revealed an adenocarcinoma. Computed tomography (CT) revealed wall thickening of the gastric antecubital region, metastatic liver tumor, and extra-regional lymph node metastasis; a diagnosis of T4a, N3a, M1 (H, LYN), and cStage IVB (HER2 3+) was confirmed. Trastuzumab, oxaliplatin, and S-1 were administered initially. After 9 months, ascites appeared, and progressive disease was diagnosed. Paclitaxel and ramucirumab were started as second-line treatments but discontinued owing to neutropenia and increasing ascites. Third-line treatment with T-Dxd was initiated, and 11 months later, CT showed the disappearance of metastases. Even after 31 months, the CR was maintained.

To the best of our knowledge, this is one of the few cases in which long-term CR was maintained with third-line T-Dxd treatment. Treatment strategies for patients with gastric cancer to achieve long-term CR require careful consideration.