Time to first treatment and optimal adjuvant treatment strategy in patients with resectable gastric cancer pathologically upstaged to lymph node-positive disease.

473 Background: Treatment strategies in resectable gastric cancer (GC) patients include perioperative chemotherapy (PEC), postoperative chemoradiation therapy (POCR), and postoperative chemotherapy (POC). Treatment delay can lead to metastases with unfavorable outcomes. We aim to identify the distribution of patients upstaged to pathologically node positive disease (pLN+) stratified by time and the optimal treatment in this cohort. Methods: We analyzed resected GC patients in the National Cancer Database (2004-2016) with clinically node negative disease (cLN-). Time from diagnosis to first definitive therapy was stratified as ≤2, >2 to ≤4, and >4 weeks. The distribution of patients upstaged from cLN- to pLN+ disease, the concordance between cLN- and pathologically lymph node negative (pLN-) disease based on treatment strategy, and time to first definitive therapy was analyzed. POC and POCR were compared to evaluate their effect on overall survival (OS) in patients with cLN- upstaged to pLN+ disease. Kaplan-Meier test, log-rank test, multivariable Cox proportional hazards analysis (MVA) were performed. Results: Of the 4,828 gastric cancer patients with cLN- disease, 514 (10.65%) patients received PEC and 4,314 (89.35%) patients received upfront surgery followed by POCR/POC. Distribution of patients stratified by time between diagnosis to first definitive treatment - chemotherapy (PEC) or surgery (POC/POCR), for ≤2 weeks was 9.5% vs. 33%, >2 - ≤4 weeks was 28.4% vs. 24.2% and >4weeks was 62% vs 42.7%, respectively. Patients upstaged from cLN- to pLN+ disease in the PEC group was 43.37%(n=206), and 70%(n=2574) in the upfront surgery group (POC/POCR). Of the 206 (43.37%) patients upstaged from cLN- to pLN+ in the PEC cohort, the upstage rate was 7.77% when chemotherapy was started within 2 weeks of diagnosis, compared to 27.67% with >2 to ≤4 weeks, and 64.56% with >4 weeks. Of the 2,574 (70%) patients upstaged in the upfront surgery cohort (POCR/POC), 30.61% were upstaged in ≤2 weeks, 24.95% in >2 to ≤4 weeks, and 44.44% in ≥4 weeks. On MVA, patients with cLN- disease that were pLN- (POCR=766, POC=341) had no significant difference in OS when treated with POCR (HR 1.11, p=0.39) compared to POC. Patients with pLN+ (POCR=2300, POC=907) disease had an association with improved OS when treated with POCR (HR 0.78, p<0.001) compared to POC. Conclusions: When resectable gastric cancer patients undergoing upfront surgery are upstaged from clinically node negative to pathologically node positive disease, postoperative chemoradiation therapy may be the optimal treatment strategy compared to postoperative chemotherapy. Clinical nodal status may not be an optimal predictor of nodal disease.