Association of low RKIP expression with poor prognosis in non-small cell lung cancer.

Abstract

3068 Background: Raf1 kinase inhibitor protein (RKIP) is able to bind Raf1 to inhibit Ras-Raf-MEK-ERK signaling, a major oncogenic pathway. It has been reported that reduced RKIP expression associates with poor prognosis in many cancers, including gastric adenocarcinoma, gliomas and bladder cancer. However, there are only several studies on its role in non-small cell lung cancer (NSCLC) and the conclusion is still controversial. Hence, we performed this study to assess the prognostic significance of RKIP in our NSCLC population. Methods: Between June 2017 and June 2020, 156 NSCLC patients treated at our hospital were included for the present study. None of the patients had received chemotherapy, radiotherapy or surgery before. Their tumor tissues and surrounding normal lung tissues were collected for immunostain and western blot analysis of RKIP expression and ERK signaling. We collected information about gender, age, histological differentiation, tumor size, TNM stage, and lymph node status. Survival curves were analyzed using the Kaplan-Meier method. Cox proportional hazards model was used to determine the prognostic value of various variables in a univariate and multivariate setting. Results: Immunostain and western blot results showed a lower RKIP expression and a higher p-ERK level in cancer tissues compared with the surrounding normal tissues. A reduced RKIP expression with high level of p-ERK was also observed in TNM stages III and IV as compared with I and II. Pearson's chi-squared test confirmed low RKIP expression associated with poorer TNM stage ( p< 0.001) and N-stage ( p< 0.05). No significant correlation was observed between RKIP expression level and gender, age, histological type or tumor size. Kaplan-Meier survival analysis revealed that patients with low RKIP expression had significantly worse overall survival than patients with high RKIP expression ( p= 0.019, log-rank). This conclusion was consistent in the stage I&II patients ( p= 0.011, log-rank) but not in the stage III&IV patients ( p= 0.711, log-rank). Univariate Cox proportional hazards regression analysis indicated Tumor size, TNM stage and RKIP expression significantly affected overall survival of the NSCLC patients. Multivariate Cox proportional hazards regression analysis confirmed RKIP expression remained a significant predictor of survival after correcting for the effects of Tumor size and TNM stage (hazard ratio = 1.730, 95% confidence interval = 1.017 – 2.942, p = 0.043). Conclusions: In this study, low RKIP expression was a poor prognostic indicator in NSCLC as it significantly correlated with poorer TNM stage, N-status, and overall survival. Our findings suggest that by inhibiting Ras-Raf-MEK-ERK pathway RKIP may play an anti-tumor role in NSCLC.