Down-regulation of beta(1C) integrin in breast carcinomas correlates with high proliferative fraction, high histological grade, and larger size.

beta(1C) integrin is an unspliced form of the integrin beta(1) subfamily, which has been shown to inhibit cell proliferation in vitro. Using an affinity-purified rabbit antibody, we have investigated 283 previously untreated breast carcinomas, with the aim of ascertaining the actual prevalence of beta(1C) expression in these tumors and of defining its pathological correlates. Immunoblotting and reverse transcriptase-polymerase chain reaction experiments have also been performed in selected cases, to confirm the immunocytochemical findings. Overall, beta(1C) immunoreactivity was down-regulated (ie, expressed in < 50% of the neoplastic cells) in 114 cases (40.3%). Down-regulation of beta(1C) expression in breast carcinomas correlated significantly with the tumor grade, the proliferative fraction (as evaluated by Ki-67 immunostaining with the MIB-1 monoclonal antibody), the estrogen and progesterone receptor status, and the tumor size (pT classification) and marginally with the node status. In a multivariate analysis with all available measures fitted simultaneously, tumor grade (P = 0.004), Ki-67 immunolabeling (P = 0.01), and pT categories (P = 0.04) were significantly associated with beta(1C) immunoreactivity. Although the short follow-up time (2-3 years) of the current series of patients does not allow the performance of survival analyses, the correlation of beta(1C) expression with tumor size, grade, and proliferative fraction and its alleged role as an upstream regulator of p27(kip1) make this integrin variant a likely novel prognostic parameter for invasive carcinomas of the breast.