Survival results by the prospectively determined clinical staging for locally advanced gastric cancer: An ancillary study of JCOG1302A (JCOG1302A2).

392 Background: Recently, neoadjuvant chemotherapy has been recognized as a promising strategy to improve the survival of patients with advanced gastric cancer. On the other hand, given the adverse events and treatment cost of chemotherapy, the candidate for NAC should be limited to patients who can benefit from NAC. In fact, as previously reported, the proportion of pathological stage I tumors was 50.4% in cT2N0, 38.7% in cT2N(+), 26.7% in cT3N0, 10.6% in cT3N(+), 9.0% in cT4aN0, and 3.0% in cT4aN(+). Therefore, clinical staging before initiation of treatment is increasingly important for determining therapeutic strategy. However, the long-term survival stratified by the prospectively-determined clinical stage has not been fully investigated. Methods: Between July 2013 and November 2014, the JCOG1302A examined 1260 patients with a clinical diagnosis of cT2/T3/T4, cN0/N1/N2/N3, M0, except for diffuse large tumors like linitis plastica and extensive bulky nodal diseases according to the Japanese Classification of Gastric Carcinoma (3rd English edition). The cT diagnosis was made by upper gastrointestinal endoscopy and comprehensive findings on upper abdominal contrast CT scan with 1 or 5 mm slice thickness. Lymph nodes with a shortest dimension greater than 8 mm or a longest dimension greater than 10 mm were defined as positive for metastasis. In this follow-up study, the survival data by stratifying the clinical staging were evaluated. Results: Among 1260 patients, survival data of 1177 were analyzed. With a median follow-up for 821 surviving patients of 6.0 years, the 5y-OS was 82.1% (95% CI, 77.3-85.9) in cT2 (n=319), 72.7% (68.2-76.6) in cT3 (n=450), 60.0% (54.9-64.7) in cT4a (n=401), and 40.0% (5.2-75.3) in cT4b (n=6), while that was 78.0% (74.2-81.2) in cN0 (n=560), 70.6% (65.4-75.2) in cN1 (n=350), 59.1% (52.5-65.1) in cN2 (n=241), and 28.4% (12.7-46.5) in cN3 (n=26), respectively. When combined with cT and cN, 5y-OS was 83.5% (77.8-87.8) in cT2N0 (n=226), 77.2% (71.0-82.2) in cT3N0 (n=232), 66.8% (56.3-75.2) in cT4aN0 (n=100), 100% in cT4bN0 (n=1), 78.7% (68.6-85.8) in cT2N(+)(n=93), 68.0% (61.1-73.8) in cT3N(+)(n=218), 57.7% (51.7-63.2) in cT4aN(+)(n=301), and 25.0% (0.9-66.5) in cT4bN(+)(n=5). Conclusions: Both the survival and the proportion of overdiagnosis of stage I patients in patients with cT4aN0, categorized as cstage IIB, was almost same as in those cT3N(+) categorized as cstage III. In considering the candidate for further treatment development of NAC with high toxic regime in future, cT3N(+) and cT4aN0 should be considered as equivalent category.