Jun Activation Domain Binding Protein 1 Expression Is Associated with Low p27^Kip1 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.