RGC after distal gastrectomy accounts for 1–2% of cases among all gastric cancers in Japan [4, 5]. RGC is rare and is commonly detected at an advanced stage, resulting in low rates of curative resection (38–40%) and consequently, a poor prognosis [6, 7]. In advanced RGC, the incidence of lymph node metastasis is high because the lymphatic vessels have been transected during the initial surgery in the remnant stomach [8]. Specially as stage III and IV RGC has a poor prognosis [6, 7], combination treatment of chemotherapy and surgery is necessary for advanced RGC, but no standard treatment guidelines are available.
Conversion surgery is an option for stage IV gastric cancer when distant metastases are controlled with chemotherapy; however, the feasibility and efficacy of conversion surgery for gastric cancer remain unclear [9]. Among patients undergoing conversion surgery, the presence of one non-curative factor before surgery and performing R0 resection are predictors of a favorable OS [10]. Accordingly, conversion surgery may result in further long-term survival of selected patients [9].
The Japan Clinical Oncology Group (JCOG) 0405 trial was a phase II clinical study of preoperative S-1 plus cisplatin (CDDP) chemotherapy for gastric cancer with PANs and/or bulky lymph node enlargement but no other distant metastases [11]. Gastrectomy with extended lymph node dissection including PAN was performed after S-1/CDDP chemotherapy. A subsequent analysis showed a 5-year survival rate of 52.7% with good prognosis [11]. According to the updated Japanese guidelines on gastric cancer [1], S-1/CDDP chemotherapy is the first-line treatment and the first-level recommendation for HER 2-negative patients. This regimen is highly emetic and requires adequate hydration to prevent renal toxicity [2].
SOX is less toxic and more convenient as the first-line treatment for advanced gastric cancer (G-SOX study), because it does not require forced hydration, unlike CDDP, compared to CS [3]. And SOX is an effective and feasible therapy for elderly patients with advanced gastric cancer and demonstrated favorable efficacy and safety compared with CS [12]; however, the patients who will benefit from conversion surgery after SOX remain unclear.
In this patient, we chose the SOX regimen because the patient was elderly and because the SOX regimen would help protect renal and cardiac function. The recommended dose of chemotherapy was reduced because the patient was elderly and had previously undergone gastrectomy.
CT revealed that PANs had decreased in size. Hence, we diagnosed that the patient achieved a partial response, but as the pathological specimens showed no cancer cells, we believed that the patient had experienced a complete pathological response. This case could not be diagnosed as a complete clinical response because the lymph node metastasis had not completely disappeared on CT, even after three courses of chemotherapy; however, the resected specimen demonstrated a complete pathological response. Thus, a complete response may be difficult for gastric cancer despite chemotherapy. Therefore, conversion therapy may be required to perform resection considering the preoperative diagnosis of metastasis.
While there have been reports of a complete pathological response after chemotherapy with CDDP, a complete pathological response after SOX chemotherapy is rare. This is the first case of advanced gastric cancer that was treated with total remnant gastrectomy after SOX chemotherapy. Thus, preoperative SOX with surgery might be an effective treatment strategy for gastric cancer with PAN metastasis.
In conclusion, we encountered a patient with advanced RGC with giant PAN who showed a complete pathological response and favorable outcome after SOX chemotherapy. The findings of this case suggest that conversion therapy with SOX chemotherapy may be one of the treatments that may result in long-term survival of patients with unresectable gastric cancer.