Basal cell carcinoma cells resemble follicular matrix cells rather than follicular bulge cells: Immunohistochemical and ultrastructural comparative studies

To detail the histogenetic relationship between basal cell carcinoma (BCC) and hair follicles, we immunohistochemically compared BCC cells to follicular matrix cells and follicular bulge cells using a panel of monoclonal antibodies against melanocytes, cytokeratins, subepidermal extracellular matrix components, and bullous pemphigoid (BP) sera, as well as using electron microscopy. Cytokeratin expression patterns were not consistent with the variety in types of cytokeratins and in cases of BCC. The distribution of some extracellular matrix components was not only linear along the interfaces of BCC tumor nests and stroma, and follicular matrix and follicular papilla; granular deposits were also seen in the stroma and follicular papilla, whereas they were only linearly distributed along the follicular bulge. The BP antigens and integrin alpha 6, which were absent in BCC and follicular matrix, were expressed in the follicular bulge area. Electron microscopically, hemidesmosomes were poorly organized in these three tissues, but the lamina densa was incomplete in BCC and follicular matrix, whereas the lamina densa in the follicular bulge area was continuous. These morphologic similarities between BCC and follicular matrix cells, and coexistence of melanocytes in the BCC tumor nest strongly suggest the differentiation of BCC toward the follicular matrix cells.