Immunohistochemical characterization of molecular classification of breast carcinoma and its relation with Ki-67

Background: Breast carcinoma is the leading cause of cancer deaths in women. Molecular classification of breast carcinoma along with Ki-67 index is considered a better predictive factor for prognosis and treatment than routine histopathology. Aims: To classify breast carcinoma into the four molecular subtypes defined by immunohistochemical expression of triple markers: Luminal A (estrogen receptor/progesterone receptor-positive [ER/PR+] and human epidermal growth factor receptor 2 HER2/neu), luminal B (ER/PR + and HER2/neu+), triple negative (ER/PR − and HER2/neu−), and HER2 positive (ER/PR−, HER2/neu+), and to correlate the expression of ER, PR, HER2/neu, and classification with Ki-67. Materials and Methods: The present study includes sixty breast carcinoma cases studied over a 3-year period. The expression patterns of ER, PR, HER2/neu, and Ki-67 were studied. Clinical features, pathologic features such as size, grade, and lymph node status, and correlation with Ki-67 of the four subtypes were compared. Results: Out of sixty cases, most common molecular subtype was triple negative (40.00%) followed by luminal B (23.33%). Most of the tumors showed low proliferative index (low Ki-67); however, triple negative and HER2 positive subtype showed high proliferative index. Most common histological subtype was ductal carcinoma which was mainly triple negative. All medullary carcinoma cases were triple negative. One case of lobular carcinoma and mucinous carcinoma each was HER2 positive and luminal B, respectively. Single case of carcinoma of male breast was luminal B subtype. Conclusion: Correlation of molecular classification with age, histological grade, and Ki-67 was statistically significant (P < 0.05). ER/PR also correlated with histological grade and Ki-67 (P < 0.01). These results emphasize the fact that molecular subtypes correlate with prognosis and aid in targeted therapy.