CCND1- and ERBB2-gene deregulation and PTEN mutation analyses in invasive lobular carcinoma of the breast

Because of the relatively low incidence of lobular breast carcinoma, there are very few studies on the molecular characteristics of this breast cancer. In an attempt to improve its characterization, we investigated in a large collection of invasive lobular carcinomas (ILCs) the status of markers known to be involved in the better-studied invasive ductal carcinomas (IDC). In the current study we disposed of 80 well-characterized ILC cases. Gene amplification of cyclin D1 (CCND1) and c-erbB2-encoding gene (ERBB2) and expression of their gene products were studied by differential polymerase chain reaction (PCR) and immunohistochemistry, respectively. A comprehensive point mutation study of the phosphatase and tensin homolog tumor suppressor gene (PTEN) was pursued by single strand conformation polymorphism (SSCP)/sequencing analysis. The CCND1 gene was rarely amplified in ILC in spite of showing overexpression of the protein in 41% of tumors. Hence, unlike IDC, increase in gene dosage did not account for the protein excess. PTEN mutations were detected in ILC (truncating mutations) in around 2% of the tumors. Unlike IDC, ILC did not display ERBB2 over-expression and expression of the transcription factor E2F1 correlated inversely with tumor grade. The observed discrepancy in the pattern of the human oncogenes CCND1 and ERBB2, which are involved in the process of carcinogenesis of ductal tumors, appears to suggest a different molecular basis for development and progression of ILC.