Jun Activation Domain Binding Protein 1 Expression Is Associated with Low p27Kip1 Levels in Node-Negative Breast Cancer

Purpose: The purpose is to evaluate expression levels of Jun activation domain-binding protein 1 (JAB1) in breast cancer tissue and adjacent normal tissue, to determine whether JAB1 expression is associated with p27 Kip1 expression in invasive breast carcinomas, and to evaluate the prognostic significance of JAB1 and p27 Kip1 in node-negative breast cancer. Experimental Design: JAB1 levels were measured in 10 matched pairs of invasive breast tumor tissue and adjacent normal tissue using Western blot analysis. We also investigated the immunoreactivity of JAB1 and p27 Kip1 levels in paraffin-embedded tissue specimens from 220 patients with node-negative breast cancer who had not received adjuvant systemic therapy. The median follow-up was 15 years. Results: JAB1 was expressed at higher levels in invasive tumors than in adjacent normal tissue ( P = 0.01). JAB1 overexpression was observed in 57% of invasive breast cancers. Low levels of p27 Kip1 were noted in 70% of the tumor specimens. We found an inverse correlation between JAB1 and p27 Kip1 expression levels ( P = 0.01). JAB1 overexpression was associated with patient age of at least 50 years ( P = 0.03) and tumor size of ≤2 cm ( P = 0.01). Elevated levels of p27 Kip1 were associated with low nuclear grade ( P = 0.01). At 5 years of follow-up, neither JAB1 nor p27 Kip1 expression was related to disease-free survival. Conclusions: These data indicate that JAB1 is commonly overexpressed in invasive breast carcinomas. JAB1 overexpression is associated with low levels of p27 Kip1 in node-negative breast cancer. In this study, JAB1 and p27 Kip1 were not independent prognostic factors.