Tumor dormancy:: Elevated expression of stanniocalcins in late relapsing breast cancer

Background: Breast cancer is known for its propensity to recur even after decades. The biology behind this phenomenon of tumor dormancy is poorly understood. The stanniocalcins (stanniocalcin-1, STC-1 and stanniocalcin-2, STC-2) are 56 kDa homodimeric proteins. They act as pro-survival factors and contribute to the endurance of terminally differentiated cells such as neurons and adipocytes. We investigated whether elevated expression of stanniocalcins also plays a part in the tumor dormancy of breast cancer. Methods: The expression of STC-1, STC-2 and estrogen receptor (ER) was studied by immunohistochemistry in 72 primary breast cancers and in their metastatic relapses detected before two years, or after 5 or 10 years from primary surgery. Results: When compared to primary tumors with early relapse and their metastases, the expression of STC-1 and STC-2 was significantly higher in relapses occurring after five year (STC-1 p = 0.0012, STC-2 p = 0.004) and even higher in very late relapses occurring 10 years after surgery (STC-1 p = 0.0017, STC-2 p = 0.0001). Moreover, primary tumors with a propensity of very late relapse displayed a higher initial expression of STC-2 (p = 0.0001). A significantly increased frequency of ER expression was found in the very late relapses. Conclusion: These findings suggest that elevated expression of STC-1 or STC-2 act as survival factors also for breast cancer cells and thereby contribute to tumor dormancy. (C) 2008 Elsevier Ireland Ltd. All rights reserved.