Positive Expression of Insulin-Like Growth Factor-1 Receptor Is Associated with a Positive Hormone Receptor Status and a Favorable Prognosis in Breast Cancer

PURPOSE: Insulin-like growth factor 1 receptor (IGF-1R) is commonly expressed in primary breast cancers. Understanding the role of IGF-1R signaling in the different subtypes of breast cancer is important because each subtype has a different outcome and requires different treatment modalities. However, the precise biological significance of IGF-1R expression in cancer cells is still unclear. In this study, we examined the expression of IGF-1R in the different molecular subtypes of breast cancer. The effects of IGF-1R expression on the survival rates and outcomes of breast cancer were also examined. METHODS: IGF-1R expression was evaluated immunohistochemically in tissue microarray blocks constructed from 1,198 invasive breast cancer samples collected from six medical institutions. IGF-1R expression was interpreted according to the human epidermal growth factor receptor 2 (HER2)/neu immunohistochemistry scoring system. Scores of 2+ and 3+ were considered positive. RESULTS: Positive IGF-1R expression was observed in 65.4% of invasive breast cancer samples. IGF-1R expression was detected in all cancer subtypes (luminal A, 84.4%; luminal B, 75.9%; HER2, 21.2%; triple-negative, 46.6%) and was found to be associated with a positive hormone receptor status and the absence of HER2 amplification (p<0.001). Positive IGF-1R expression was significantly associated with high survival rates (p=0.014). However, a multivariate analysis revealed that the expression levels of IGF-1R did not achieve statistical significance. In the triple-negative cancer subtype, IGF-1R expression was found to be associated with a lower disease-free survival rate (p=0.031). CONCLUSION: Positive IGF-1R expression is associated with a favorable prognosis in breast cancer. IGF-1R is frequently expressed in the luminal A/B subtypes of breast cancer, and its expression is related to the hormone receptor status.