IMP3 is a novel biomarker for triple negative invasive mammary carcinoma associated with a more aggressive phenotype

IMP3, an oncofetal protein, is a member of the insulin-like growth factor-II (IGF-II) mRNA-binding protein family. Its relevance as a novel biomarker in lung, pancreatic, renal, and cervical adenocarcinoma was recently revealed. However, its role in breast carcinogenesis and tumor progression is not yet established. Basal-like carcinoma was initially identified by gene expression profiling. It accounts for 15% to 30% of all breast cancers. These tumors express basal epithelial markers including cytokeratin 5 but lack expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2), therefore, are often referred to as triple negative breast cancer. They have been found to be associated with a worse overall and disease-free survival. In this retrospective study, we examined the IMP3 expression in invasive ductal carcinoma of the breast and correlated its expression with morphological and biologic prognostic factors. The study group comprised 138 cases of invasive ductal carcinoma retrieved from the surgical pathologic files for a 10-year period from 1997 to 2006. Survival data and clinical stage were available on all 138 patients. Tumor characteristics including size, grade, lymphovascular invasion, necrosis, lymph node metastasis, estrogen receptor, progesterone receptor, and HER2 status were obtained from pathologic reports. Immunohistochemistry was performed on formalin-fixed paraffin-embedded tissue using mouse monoclonal antibody against IMP3 and CK5/6. Of the 138 breast cancer cases, IMP3 expression was seen in 45 (33%). Twenty-five of the IMP3+ cases were triple negative. We found significant correlation between IMP3 expression and higher grade (P = .001), necrosis (P< .0001) triple negative, and CK5/6 expression (P < .0001 for each). Cox multivariate analysis showed a hazard ratio of IMP3 expression at 3.14 (P = .05). IMP3 is a novel biomarker for triple negative (basal-like) invasive mammary carcinoma, and its expression is associated with a more aggressive phenotype and decreased overall survival.