Background: Metastasis of malignant breast cells is in part mediated through degradation of the extra-cellular matrix by proteolysis, enabling malignant cells to migrate through the surrounding stroma. Heparanase-1 (HPR1) is an endoglycosidase that specifically degrades the heparan sulfate (HS) moiety of proteoglycans, a component of the extracellular matrix and basement membrane.
Methods: Fifty-one primary breast tumors, 13 lymph node metastases, 4 ductal carcinoma in situ, 7 benign, and 5 normal specimens were examined for HPR1 expression using immunohistochemical staining. The functional role of HPR1 expression was determined by examining HS deposition using immunofluorescence staining.
Results: Sixteen of 30 breast carcinomas (53%) with sentinel node metastasis expressed HPR1. In contrast, only 5 of 21 nonmetastatic primary breast carcinomas (23%) were HPR1 positive. Eighteen of 30 breast carcinomas between 1 and 5 cm expressed HPR1, compared with 3 of 21 HPR1-positive specimens in tumors < or =1 cm. Statistical analysis revealed that HPR1 expression was associated with breast tumor metastases (P =.04) and primary tumors between 1 and 5 cm (P =.002). Ninety percent of HPR1-positive tumors lacked HS deposition, suggesting an inverse correlation between HPR1 expression and HS deposition.
Conclusions: HPR1 expression correlates with the lack of HS deposition and with the metastatic potential of breast cancers. The frequency of HPR1 is significantly higher in breast tumors between 1 and 5 cm than in tumors < or =1 cm.