Interferon regulatory factor-1 (IRF-1), human X-box binding protein-1 (hXBP-1), nuclear factor kappa B p65 (NFκB p65) and nucleophosmin (NPM) have been implicated in a signaling network of endocrine responsiveness. Expression of these proteins was measured by immunohistochemistry in tissue microarrays of 54 breast tumors. Correlations between each protein and established prognostic markers were assessed by Spearman's rank order correlation coefficient and partial correlation coefficient analyses. Moderate/strong staining is seen for hXBP-1 (79% of tumors) and NFκB p65 (57%). NPM exhibits nuclear staining (95%); IRF-1 exhibits both cytosolic (IRF-1c; 90%) and nuclear staining (IRF-1n; 51%). IRF-1c is associated with age (p=0.034); IRF-1n and PgR expression are correlated (p=0.014). NFκB p65 shows a borderline association with S phase (p=0.062). Coexpression of IRF-1c and hXBP1 (p=0.001), IRF-1c and NFκB (p=0.002), and hXBP-1 and NFκB (p=0.018) is observed. An inverse correlation exists between IRF-1n and NFκB (p=0.034). All four proteins are detected in breast tumors and their expression patterns support their role(s) in a key signaling network.

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