Pre-Paget cells express a Paget cell marker before losing a keratinocyte marker.

Extramammary Paget's disease (EMPD) is a cancer of the anogenital epithelium. Its origin has been variously attributed to keratinocytes or to Toker cells. Slides of 3 advanced cases of EMPD were incubated with trypsin to retrieve antigens. The slides were then stained with rabbit polyclonal anti-carcinoembryonic antigen to mark Paget cells and mouse monoclonal anti-cytokeratin 10 to mark keratinocytes. Several cells in each case stained with both the Paget cell marker and the keratinocyte marker. The presence of cells with both markers shows that Paget cells originate from keratinocytes. The presence of pre-Paget cells in advanced cases of EMPD shows that Paget cells are continuously recruited from keratinocytes.