Phospholipase C-? Immunostaining in Human Breast Carcinoma: Clinical Significance and Correlations with Protease and Growth-Factor Receptor Species

Abstract

: Cryostat sections of 73 invasive breast carcinomas were immunostained with a rabbit polyclonal antibody to phosphoinositide-specific phospholipase C-γ (PLC-γ), an enzyme that mediates signal transduction in tyrosine kinase growth-factor pathways. Degree of immunoreactivity was then correlated with clinicopathologic data (stage, ER status, recurrence) and immunostaining for tyrosine kinase growth-factor receptors (EGFR, ERBB-2) as well as selected “invasion-associated” proteases (cathepsin D, urokinase plasminogen activator, matrix metalloproteinases 2 and 9 [MMP-2, MMP-9]). Neoplastic epithelial populations were PLC-γ immunoreactive in 95% of tumors although staining was focally distributed (in <50% of cells) in 51% of positive cases. Forty-four percent also exhibited immunostaining of peritumoral, spindle-shaped cells (i.e., fibroblasts, endothelium, inflammatory cells). The degree of PLC-γ immunoreactivity in neoplastic epithelium was not significantly correlated with clinicopathologic features, growth factor receptor overexpression, or protease immunostaining. Stromal cell PLC-γ staining, however, was significantly associated with stromal cell immunoreactivity for cathepsin D (p = 0.03), urokinase plasminogen activator (p = 0.01), and MMP-2 (p = 0.04). Disease recurrences were also more frequent in tumors with stroma/spindle cell PLC-γ immunoreactivity (66% vs. 41%, p = 0.04). We conclude that PLC-γ immunostaining, compatible with increased tyrosine kinase pathway signaling activity, is observed not only in a high proportion of neoplastic breast epithelial populations but also in accompanying stromal cell populations in a significant number of cases. Concordance with protease immunoreactivity among peritumoral stromal cells suggests that tyrosine kinase signaling may participate in protease elaboration in vivo, possibly conferring aggressive clinical behavior.