Background: There is a need for reliable predictors of breast cancer aggressiveness that will further refine the staging classification and help guide the implementation of novel therapies. We have identified RhoC as being nearly always overexpressed in the most aggressive form of breast cancer, inflammatory breast cancer (IBC); in subsequent work we identified RhoC to be a promising marker of aggressive behavior in breast cancers less than 1 cm in diameter. We hypothesized that RhoC expression would identify aggressive, non-IBC tumors breast cancer patients at any stage with worse outcomes defined as recurrence and/or metastasis.
Methods: We constructed four high-density tissue microarrays (TMAs) using 801 tissue cores from 280 patients. These tissues represent a wide range of normal breast and breast disease, including intraductal hyperplasia, ductal carcinoma in situ (DCIS), invasive carcinomas, and distant metastases. The TMAs were immunostained using a polyclonal anti-RhoC antibody developed in our laboratory. Cytoplasmic RhoC expression was scored as negative, weak, moderate, or strong by a previously validated scoring schema.
Results: RhoC expression increases with breast cancer progression. All samples of normal breast epithelium had negative to weak staining, whereas staining intensity increased in hyperplasia, DCIS, invasive carcinoma, and metastases (Kruskal-Wallis p < 0.001). In patients with invasive carcinoma, high RhoC expression was associated with features of aggressive behavior including high histologic grade, positive lymph nodes, and negative hormonal receptor status. High RhoC expression was a predictor of overall survival in patients with breast cancer (log rank test, p = 0.002) and was associated with 100% increase in the risk of death as compared to patients with low RhoC expression. Importantly, high RhoC was an independent predictor of poor response to doxorubicin-based chemotherapy with a hazard ratio of 3.1 and a 95% CI of 1.2-7.7 (p = 0.02).
Conclusion: RhoC expression increases with breast cancer progression and RhoC protein level in tumor tissue is strongly associated with biologically aggressive invasive carcinomas of the breast. RhoC expression, if validated, may identify patients who are less likely benefit from doxorubicin therapy and suggests RhoC overexpression as a new target for intervention.