Low expression of SLC22A18 predicts poor survival outcome in patients with breast cancer after surgery

Purpose: The aims of this study were to evaluate the relationship between SLC22A18 expression and clinicopathologic features while investigate the prognostic value of SLC22A18 expression in breast cancer after surgery. Specimens and methods: Immunohistochemistry was used to examine SLC22A18 protein expression in the breast tumors. Prognostic value of SLC22A18 protein and other clinicopathologic factors were evaluated. The Kaplan–Meier method and the Cox proportional hazards model were used to predict factors with a significant independent prognostic value. Digital image analysis was employed to quantify immunostaining. Results: SLC22A18 expression was correlated with tumor size, lymph node metastasis, clinical stage, and extensive lyphovascular invasion. The results of Kaplan–Meier analysis indicated that SLC22A18 expression was associated with relapse-free survival (RFS) of breast cancer. The survival of higher expression SLC22A18 group had longer cum survival compared to the group with low expression. The difference was significant (p = 0.003, log-rank test). Cox's regression analysis showed that tumor size, lymph nodes metastasis, nuclear stage, extensive lymphovascular invasion, and SLC22A18 expression might be used as prognostic factor for RFS. Nuclear stage and SLC22A18 expression were the most meaningful histopathologic parameter in predicting tumor recurrence. Compared with the group of higher SLC22A18 expression, the lower expression group was more likely to relapse. The HR is 2.624 (p = 0.035). Conclusion: Low expression of SLC22A18 was associated with tumor progression, recurrence and poor survival after breast surgery. Testing expression of SLC22A18 will be helpful for predicting prognosis in breast cancer.