CD9 Expression in Tumor Cells Is Associated with Poor Prognosis in Patients with Invasive Lobular Carcinoma

Purpose: We investigated the prognostic significance of CD9 expression in tumor cells of patients with invasive lobular carcinoma (ILC). Methods: CD9 expression was evaluated by immunohistochemistry in 113 ILC tissue samples. Correlation of CD9 expression with the patients' clinicopathological parameters and overall survival was assessed. Results: CD9 expression was detected in 48 (42.5%) ILC patients. However, no significant relation could be determined between CD9 expression and the clinicopathological parameters of the patient including tumor size, lymph node metastasis, lymphovascular invasion, histologic grade, expression of hormone receptors, human epidermal growth factor receptor 2 status, and Ki-67 labeling index. Patients with CD9 expression had worse overall survival (p = 0.051) and disease-free survival (DFS, p = 0.014) compared to patients without CD9 expression. Multivariate analysis revealed that CD9 expression was an independent prognostic factor for DFS (p = 0.049). Conclusion: CD9 expression in tumor cells could be a significant prognostic marker in patients with ILC.