Invasive Micropapillary Carcinoma of the Breast: Immunophenotypic Analysis and Role of Cell Adhesion Molecules (CD44 and E-Cadherin) in Nodal Metastasis.

Invasive micropapillary carcinoma is a morphologically distinct subtype of breast carcinoma with high frequency of lymph node metastasis. In this study, we analyzed clinicopathologic features, immunophenotype, and expression of adhesion molecules [CD44 and E-cadherin (E-Cad)] in pure invasive micropapillary carcinoma of the breast. All cases had diffuse micropapillary pattern and were grade II tumors. Lymphovascular emboli were present in 80% and lymph node tumor deposits were seen in 69.2% cases. The cases were classified as; luminal A (11 cases), luminal B (8 cases), Her-2-neu overexpressing (4 cases), and triple negative (2 cases). All cases were positive for luminal cytokeratin (CK)CK8/18, and 2 cases showed <10% positivity for CK5/6. Eighteen cases showed loss of CD44 expression and 7 cases showed only weak positivity. Seven cases with lymph node metastasis showed reexpression of CD44 at metastatic site. Strong to moderate expression of E-Cad was observed in all cases and the corresponding nodal metastasis. To conclude, the loss of the CD44 expression plays role in lymphovascular permeation and metastasis and it can be hypothesized that its reexpression at metastatic site may play a role in homing of tumor cells. However, intact E-Cad expression could be because of the fact that tumour cells travel as clusters and retain their expression of E-Cad.