The standard form of CD44 as a marker for invasion of encapsulated papillary carcinoma of the breast.

Encapsulated papillary carcinoma (EPC), a rare variant of papillary carcinoma of the breast, is regarded as a transition form between carcinoma in situ and invasive carcinoma. Here, we tried to identify differences in immunohistochemical phenotype between 10 EPCs with invasive properties (EPC with invasion) and 17 non-invasive EPCs (EPC). We immunohistochemically assessed the expression of hormone receptors, matrix metalloproteinase (MMP) 2 and MMP9, vascular endothelial growth factor (VEGF), CD31, and D2-40, markers of tumor-associated macrophages (CD163, CD206), Ki-67 and stem cell markers (CD44 and CD24). The frequency of MMP9-positive cases and the number of tumor-associated macrophages infiltrating into the fibrous capsule were significantly higher in EPC with invasion than in EPC. The expression of the standard form of CD44 (CD44s) was significantly stronger in EPC with invasion than in EPC (P = 0.0036) and was correlated with MMP2 expression and M2-like macrophage infiltration. A multivariate logistic model analysis showed that CD44s expression in tumor cell and infiltration of CD163 positive macrophage in EPC capsule showed an independent odds ratio for invasion of EPC. Thus, CD44s may be a potential marker predicting invasive potential of EPC and could play an important role in progression to the invasive phase of EPC.