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Abstract：
No standard treatment has been established for gastric neuroendocrine carcinoma (G-NEC). We present the case of a patient with recurrent G-NEC who achieved a complete response (CR) with nivolumab. A woman in her 70 s, with no significant medical or family history of illness, underwent an upper gastrointestinal endoscopy, which revealed a Borrmann type 2 tumor in the gastric antrum. Malignant tumor cells were not detected in the endoscopic biopsy samples; however, a malignant gastric tumor was strongly suspected. Therefore, surgical resection was performed, and the tumor was pathologically diagnosed as a G-NEC with liver metastases. Adjuvant etoposide plus carboplatin was administered for four cycles, but recurrence in the liver was observed 5 months after the completion of adjuvant chemotherapy. Ramucirumab plus paclitaxel and irinotecan were introduced as second and third-line treatments. After these treatments, the mesenteric lymph node metastases expanded. Tumor mutation burden (TMB) was low (five mutations/megabase), and microsatellite instability remained stable. However, programmed death-ligand 1 Combined Positive Score (CPS) was ≥ 5 in the resected sample. Therefore, nivolumab monotherapy was introduced as a fourth-line treatment. The mesenteric lymph node metastases exhibited swelling 3 weeks after the initiation of nivolumab; however, they rapidly shrank, and CR was later achieved. Treatment with nivolumab is currently ongoing for 12 months. This is the first report of nivolumab monotherapy in a patient with G-NEC who showed pseudo-progression. Even in TMB-low and microsatellite stable cases, nivolumab may be a viable option for patients with G-NEC.
摘要：
尚未建立针对胃神经内分泌癌（G-NEC）的标准治疗方法。我们介绍了一例复发性G-NEC患者，该患者使用nivolumab实现了完全缓解（CR）。一个70多岁的女人，没有明显的病史或家族史，做了上消化道内窥镜检查,显示胃窦有Borrmann2型肿瘤.在内窥镜活检样本中未检测到恶性肿瘤细胞；然而，强烈怀疑恶性胃肿瘤。因此,进行了手术切除，病理诊断为G-NEC伴肝脏转移。辅助依托泊苷加卡铂四个周期，但在辅助化疗完成后5个月观察到肝脏复发。ramucirumab联合紫杉醇和伊立替康被引入作为二线和三线治疗。经过这些治疗,肠系膜淋巴结转移扩大。肿瘤突变负荷（TMB）低（5个突变/兆碱基），微卫星不稳定性保持稳定。然而,在切除的样本中，程序性死亡-配体1联合阳性评分（CPS）≥5。因此,引入nivolumab单药治疗作为四线治疗.肠系膜淋巴结转移在nivolumab开始后3周出现肿胀；然而，他们迅速萎缩，CR后来实现。nivolumab的治疗目前正在进行12个月。这是纳武单抗单一疗法在G-NEC患者中的第一份报告，该患者表现出假性进展。即使在TMB低和微卫星稳定的情况下，纳武单抗可能是G-NEC患者的可行选择.
