The optimal extent of lymph node dissection for gastric cancer with para-aortic lymph node metastases.

413 Background: Gastric cancer (GC) with para-aortic lymph node (PAN) metastasis is diagnosed as stage IV and basically treated with chemotherapy. Recently, D2 and PAN dissection after neoadjuvant chemotherapy (NAC) was reportedly effective when PAN metastasis was limited within #16a2/b1 area. However, PAN dissection is highly invasive surgical procedure and it still remains unclear whether PAN dissection contributes to the survival for these tumors. This study aimed to determine the optimal extent of lymph node dissection for these tumors focusing on survival benefit of PAN dissection. Methods: The study examined patients who received radical gastrectomy with D2 and PAN dissection after NAC for gastric cancer with PAN metastasis (#16a2/b1) from 2004 to 2015. Survival benefit of lymph node dissection was estimated using therapeutic value index (TI). TI was calculated by multiplication of incidence of metastasis and 5-year survival rate of patients with metastasis for each lymph node area. TI of D2 dissection area (TI-D2) and PAN area (TI-PAN) was calculated separately. Overall survival (OS) was calculated in patients who had metastasis to PAN pathologically after surgery (pPAN+ group) and those who had not (pPAN- group). The recurrence site was also examined. Results: Thirty-two patients were analyzed. TI-D2 and TI-PAN were 15.6 and 0.0, respectively. 5y-OS was 81.0% in pPAN- group (21 cases) but was 0.0% in pPAN+ group (11 cases). The most frequent recurrence site was the lymph nodes (82.4% of all recurrences). Among lymph node recurrence, almost all recurrence patterns included the PANs (85.7% of lymph node recurrence). Conclusions: The prognosis was extremely poor when tumor cells remained on PAN after NAC. In these cases, PAN recurrence was seen most frequently even after PANs had been dissected. Patients with PAN could have the chance for the cure only when tumor cells on PAN was completely eliminated by NAC. It is unclear whether they actually needed PAN dissection for pathologically negative PAN. The optimal extent of lymph node dissection after NAC might be D2 for GC with PAN metastasis.