Differential heparanase-1 expression in malignant and benign pheochromocytomas

Extracellular matrix (ECM) degradation is an essential step that allows tumor cells to penetrate a tissue barrier and become metastatic. Heparanase-1 (HPR) is an endoglycosidase that specifically degrades heparan sulfate proteoglycans, a chief component of the ECM. Previous studies have demonstrated HPR expression in various malignancies and that there is differential HPR expression between benign and malignant tumors. Currently, there is no technique that can reliably predict the malignant behavior of some pheochromocytomas. This study tests whether HPR is differentially expressed in malignant and benign pheochromocytomas.

Paraffin-embedded specimens from 29 pheochromocytomas were evaluated. The tissues were collected from surgical specimens over a 10-year period from 26 patients (8 males, 18 females) with a mean age of 47 years (range 19-78 years, median 47 years). One female patient underwent 3 separate operations for malignant pheochromocytoma and thus provided 3 specimens. Another female patient had both the primary tumor and a liver metastasis processed, and therefore provided 2 specimens. Patient charts and pathology reports were reviewed to classify the pheochromocytomas as either benign or malignant. Based on clinical behavior and/or pathological evidence of metastasis or invasion into surrounding tissues, 10 specimens were malignant and 19 had benign behavior. As a control, normal adrenal tissue from 3 nephrectomy specimens was included in the study, as was tissue from 1 adrenocortical adenoma. All 33 specimens were tested for HPR gene expression by in situ hybridization (ISH) with an antisense RNA probe and immunohistochemistry (IHC) with an anti-HPR antibody. Statistical analysis was done using the chi(2) test of proportions to determine if HPR expression correlated with malignancy using ISH, IHC, or both tests together.

Using ISH, the percentage of HPR expression in the malignant pheochromocytomas was 50% while HPR expression in the benign tumors was 21% (P = 0.11). Using IHC, the percentage of HPR expression in the malignant pheochromocytomas was 80% while HPR expression in the benign tumors was 32% (P = 0.01). Considering both tests cumulatively, all 10 malignant pheochromocytomas stained positive for HPR by ISH and IHC, while only 37% of the benign tumors were positive for HPR expression (P = 0.001). The one adrenal adenoma and the 3 normal adrenal glands processed stained negative for HPR expression by both ISH and IHC.

HPR expression is higher in malignant pheochromocytomas than in benign pheochromocytomas or normal tissue. HPR may contribute to the invasive characteristics of malignant pheochromocytomas and might be used as a marker to distinguish malignant from benign pheochromocytomas. HPR expression might also be used as a prognostic tool in guiding long-term patient follow-up.