Methionyl-tRNA synthetase and aminoacyl-tRNA synthetase interacting multifunctional protein 2 exon 2 deletion variant as diagnostic markers for endobronchial ultrasound-guided brushing cytology in lung cancer

Abstract

Background: Methionyl-tRNA synthetase (MARS) initiates translation by transferring methionine to the initiator tRNA, and its overexpression is associated with cancer growth. Aminoacyl-tRNA synthetase interacting multifunctional protein 2 exon 2 deletion variant (AIMP2-DX2) interrupting the tumor-suppressive activity of AIMP2 is also overexpressed in lung cancer. Thus, it can be a useful biomarker for lung cancer diagnosis. In the era of low-dose computed tomography screening for early detection of lung cancer, it is critical to diagnose peripheral lung nodules accurately and safely. In this study, we evaluated the clinical application of new diagnostic staining methods using MARS and AIMP2-DX2 in patients suspected of having lung cancer. Methods: Immunohistochemistry for MARS was performed on lung tissues from wild-type mice, lung cancer mouse models, and surgical specimens from lung cancer patients to evaluate the expression of MARS in cancer tissues. The expression of MARS gene in single cells was also analyzed to show the difference between cancer cells and non-cancer cells. Samples obtained by radial endobronchial ultrasound-guided brushing were processed for cytological examination. Then, double staining with MARS and AIMP2-DX2 antibodies was measured by immunofluorescence in the cytology samples for peripheral lung nodules. Diagnostic performance was compared against biomarkers. Results: MARS was strongly expressed in mouse and human lung cancer tissue compared with non-neoplastic lung tissue. In addition, MARS gene was frequently overexpressed in the malignant cells compared to benign cells. For the clinical study, 113 patients were enrolled during the study period. MARS staining was the only independent staining method for the prediction of malignant cells (adjusted odds ratio: 6.02, 95% confidence interval: 1.32–28.09). The sensitivity, specificity, and accuracy was 72%, 65%, and 71% for adding MARS staining with cytology, respectively, compared with 31%, 100%, and 47% for conventional cytology alone. The area under the curve (AUC) for cytology, MARS, and MARS plus cytology was 0.64, 0.68, and 0.69, respectively. Conclusions: The combination of MARS staining with cytology showed increased sensitivity and accuracy for diagnosing indeterminate lung nodules on chest computed tomography scans. However, we could not prove a significant improvement in the AUC in the MARS staining method due to its lower specificity compared to conventional cytology.