Abstract
E-cadherin (E-CD) inactivation with loss of E-CD-mediated cell adhesion is the hallmark of lesions of the lobular phenotype. E-CD is typically absent by immunohistochemistry in both lobular carcinoma in situ (LCIS) and invasive lobular lesions, suggesting it occurs early in the neoplastic process. In laboratory models, downstream post-transcriptional modifiers such as TWIST and SNAIL contribute to the dissociation of the intracellular component of the cadherin-catenin complex (CCC), resulting in tumor progression and invasion. We hypothesized that complete CCC dissociation may play a role in lobular neoplasia progression. Here we explore the relationship between loss of E-CD and dissociation of the CCC in pure LCIS and LCIS associated with invasive cancer. Fresh-frozen tissues were obtained from 36 patients undergoing mastectomy for pure LCIS (n = 11), LCIS with ILC (n = 18) or LCIS with IDC (n = 7). Individual lesions were subject to laser-capture microdissection and gene-expression analysis (Affymetrix HG-U133A 2.0). Immunohistochemistry for ER,PR,HER2, E-CD,N-CD,α-,β-, and phosphoβ-catenin, TWIST, and SNAIL were evaluated in normal, in situ, and invasive components from matched formalin-fixed paraffin-embedded samples (n = 36). CCC-dissociation was defined as negative membranous E-CD, α- and β-catenin expression. E-CD was negative in all LCIS and ILC lesions, and positive in all normal and IDC lesions. Membranous α and β-catenin expressions decreased with the transition from LCIS to ILC (pure LCIS 82%; LCIS w/ILC 28%; ILC 0%), while TWIST expression increased (pure LCIS low; LCIS w/ILC moderate; ILC high). Gene expression paralleled IHC-staining patterns with a stepwise downregulation of E-CD, α and β-catenins from normal to LCIS to invasive lesions, and increasing expression of TWIST from normal to LCIS to ILC. Loss of E-CD expression is an early event in lobular neoplasia. Decreasing membranous catenin expression in tandem with increasing levels of TWIST across the spectrum of lobular lesions suggests that CCC dissociation is a progressive process.