Gluteal muscle metastasis with peritoneal dissemination from gastric cancer during postoperative adjuvant chemotherapy: a case report.

BACKGROUND: Skeletal muscle metastasis from gastric cancer is rare and has a poor prognosis. We reported a case of gluteal muscle metastasis with peritoneal dissemination from gastric cancer during postoperative adjuvant chemotherapy. CASE PRESENTATION: A 64-year-old man with gastric cancer underwent distal gastrectomy with D2 lymph node resection. The pathological diagnosis was poorly differentiated adenocarcinoma and signet cell carcinoma, T3N3bM0, Stage IIIC. Metastases were found in all regional lymph nodes, except 11p. The resection margin was negative. S-1 plus docetaxel therapy was administered as postoperative adjuvant chemotherapy. Six month post-operation, the patient presented with right gluteal muscle tenderness and abdominal distension. Computed tomography revealed a solid mass in the right gluteal muscle, a disseminated nodule on the abdominal wall, and massive ascites. Pathological examination of the gluteal muscle revealed signet cell carcinoma, similar to the resected gastric cancer. The tumor was diagnosed as gastric cancer metastases. Ascites cytology was class V. Thereafter, the patient underwent one course of capecitabine plus cisplatin combined with trastuzumab. Radiation therapy was also administered to relieve the pain of gluteal muscle metastasis. However, chemoradiotherapy was ineffective, and the patient died 2 months after the recurrence. CONCLUSIONS: Skeletal muscle metastasis and peritoneal dissemination during adjuvant chemotherapy indicated a poor prognosis.