Lymph node micrometastasis of poorly differentiated node-negative gastric cancer risks a worse-than-expected survival outcome under standard management algorithm

Background Investigation of lymph node micrometastasis (mN) of gastric cancer has been focused on either T1 disease or T1-4N0 disease. Yet, it is unclear whether standard management algorithm toward poorly differentiated gastric cancer (PDGC) is more vulnerable to existence of mN, given its inherently biological aggressiveness, as compared with other histological types. Patients and methods A surgical series (n = 3456) of gastric cancer categorized by histological differentiation was enrolled to analyze survival stratification. Of them, a cohort of T1-T4 N0 PDGC (n = 100) were subjected to cytokeratin immunohistochemistry, a surrogate of mN. Results Cancer-specific survival by AJCC8 staging system could be nicely differentiated in both well-/moderately differentiated and signet ring cell types, while those between stage IA versus IB (p = 0.105), and stage IB versus IIA (p = 0.141) in PDGC could not. Thirteen (13%) out of 100 node-negative PDGC cases exhibited mN, with 5, 2, 5 and 1 cases occurring in T1, T2, T3, and T4 stage, respectively, without identifiable contributing factors. Prognostic performance of AJCC8 working upon PDGC became more discriminative by incorporating mN, as hazard ratio of stage IIIC referenced to stage IA increased from 43 to 78. Conclusion Defective discriminative survival of PDGC by standard staging algorithm prompted us to survey mN occurring in T1-T4N0 PDGC. The prognostic performance of AJCC8 working upon PDGC was enhanced by incorporating mN. As so, we recommend documentation of mN exclusively on node-negative PDGC that helps unveil stage migration phenomenon and switch to appropriate adjuvant therapy in need.