The role of HER-2/neu oncogene and vimentin filaments in the production of the Paget's phenotype.

The histogenesis as well as the biological and molecular differences in mammary Paget's disease (MPD) and extramammary Paget's disease (EPD) are not well understood. HER-2/neu oncogene overexpression is associated with poor prognosis in breast cancer patients. It is also believed that the spread of Paget's cells through the epidermis is induced by a motility factor that acts via the HER-2/neu receptor. However, previous studies on HER-2/neu expression in MPD and EPD have given conflicting results. Recent studies have suggested that vimentin expression in breast cancer confers a more aggressive phenotype with a possible role in tumor invasion and metastasis. We examined 58 cases of MPD and EPD for HER-2/neu overexpression and vimentin status to study the role of these markers in the production of the Paget's phenotype. Thirty-five of the 38 cases (92.1%) of MPD were associated with an underlying carcinoma, while none of the cases of EPD were associated with an underlying malignancy. Thirty-six of the 38 cases of MPD (94.7%) overexpressed the HER-2/neu oncoprotein and 17 cases (44.7%) showed vimentin expression. In contrast, only 1 of the 20 cases of EPD (5%) showed positivity for HER-2/neu oncoprotein and all were negative for vimentin. Our results indicate that the cell motility enhancing effect of HER-2/neu oncoprotein and possibly vimentin plays a significant role in the pathogenesis of MPD which appears to be a pagetoid spread of an underlying ductal malignancy (secondary), while EPD is an in situ malignant transformation of a totipotential epidermal cell or glandular epithelium.