Background: Lysyl-tRNA synthetase (KRS) is an aminoacyl-tRNA synthetase (ARS) that is essential for protein synthesis during ligation of specific amino acids to their cognate tRNAs. Aberrant expression of ARSs is associated with various human cancers. Methods: Using immunohistochemical detection, the present study analyzed the clinical relevance of KRS expression in tumor cells and tumor-associated inflammatory cells (TAI) in 457 patients who underwent curative radical surgery and standard adjuvant therapy and who were observed on long-term follow-up. Results: High expression of KRS in tumor cells (tumor-KRS(+)) was noted in 43.3 % (198 of 457) of cases. High expression of KRS in tumor-associated inflammatory cells (TAI-KRS(+)) including macrophages/monocytes, CD4-positive T cells, and/or neutrophils was observed in 37.2 % (170 of 457) of cases. Status of KRS in the tumor and TAI revealed an association with the known clinicopathological parameters for prognosis of gastric cancer. Tumor-KRS(+) status correlated to shorter overall survival, especially in stage III to IV cancers (P = 0.003), while TAI-KRS(+) status correlated significantly to longer overall survival in gastric cancer (P = 0.049). Cases with tumor-KRS(+) and TAI-KRS(-) status showed significantly reduced survival rates compared to those of other cases (P = 0.010), and status of tumor-KRS(+) and TAI-KRS(-) was revealed as an independently poor prognostic factor of overall survival (P = 0.001). Conclusions: KRS-related inflammation can be identified in a subset of gastric cancer. This may be a possible mechanism of immune surveillance against tumor progression. In addition, expression status of KRS in tumor and TAI may be an independent prognostic marker for gastric cancer patients.
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