Evaluation of CD9 Expression of Tumour Cells and Stromal Immune Cells in Breast Carcinoma by Immunohistochemistry

Introduction: Cluster of Differentiation 9 (CD9), known as Motility Related Protein (MRP-1) regulates cell adhesion, motility, migration and proliferation. Many studies have stated conflicting results on prognostic significance of invasive breast carcinomas with CD9 expression that had performed on tumour tissues. Aim: To assess the inter-relationship of CD9 expression of tumour cells and stromal immune cells in breast carcinoma with clinicopathological parameters which include age, tumour size, grade, histological type, lymph nodes, tumour staging and molecular classification. Materials and Methods: An observational prospective (July 2020 to June 2021) and retrospective (October 2019 to June 2020) study was done in 71 cases of resected primary invasive breast carcinoma over a period of one and half year at Sri Devaraj Urs Medical College, Karnataka, India. Immunohistochemistry (IHC) staining was done using CD9 antibody. Tumour cells (T-CD9) expression was evaluated by Immunoreactivity scoring (IS= Intensity score×Extent of staining). The stromal cells (S-CD9) expression was evaluated by percentage (%) of stromal area occupied by CD9 stained immune cells. Chi-square test was used as test of significance for qualitative data. The p-value of <0.05 was considered as statistically significant. Results: Out of 71 cases, T-CD9 expression was noticed in 40 (56.34%) cases and IS <4 considered as negative was observed in 31 (43.66%) cases. However there was no association with age, tumour size, grade and molecular markers for the expression of both T-CD9 and S-CD9. Human Epidermal growth factor receptor 2 neu (HER2neu) negative was associated with T-CD9 expression (p-value=0.05). Hence, CD9 can be used as prognostic marker for Her2neu negative cases. Conclusion: The CD9 expression was not significantly associated with tumour cells (T-CD9) and stromal cells (S-CD9) in breast carcinoma cases. However, it was significantly associated with Her2neu negative tumour cells. T-CD9 showed more positivity in Luminal A followed by triple negative, whereas S-CD9 showed more positivity in Luminal B. CD9 did not show association with any parameters except Her2neu negative