Gastric neuroendocrine carcinoma presenting complete durable response by nivolumab treatment for multiple metastases and radiotherapy to oligoprogressive metastasis.

Gastric neuroendocrine carcinomas (NEC) are highly aggressive cancer with dismal prognosis. Platinum-based chemotherapy is used as the first-line treatment for this entity. However, there are no established therapeutic guidelines for platinum-resistant gastric NEC. We herein report a patient with metastatic gastric NEC who achieved durable and complete response to nivolumab with radiotherapy for oligoprogressive metastasis. A 70-year-old male patient had recurrences of resected gastric NEC, involving the liver and lymph nodes. His disease became refractory to cisplatin and etoposide combination therapy, after which he was treated with nivolumab. All the tumors showed marked shrinkage. However, 1 year after starting nivolumab, one metastatic lesion of the liver began to enlarge, and radiotherapy was performed to the lesion. Thereafter, a complete response was obtained, which has been maintained without any treatment for the past 2 years.