Introduction: Merkel cells (MC) are neuroendocrine cells of skin present in both the epidermal basal layer and the outer root sheath of hair follicles. Immunohistochemical studies revealed an increase of their number in hyperplastic and neoplastic lesions of skin. In this paper, we investigated the distribution of MC among adnexal skin tumors and their possible relationship to proliferative activity of the tumor epithelium. Material and methods: We investigated 76 tumor specimens with hair follicle differentiation. Paraffin-embedded tissue and cryo-preserved tissue samples were available for immunohistology using the alkaline phosphatase - anti-alkaline phosphatase (APAAP) technique with antibodies against simple-type cytokeratins to identify MC. In addition, antibodies against MIB-1 and proliferating cell nuclear antigen (PCNA) were applied to evaluate the proliferative activity of the tumors. Results: The tumors with the highest proliferative activity like infundibular tumor, hair follicle nevus, trichofolliculoma were also the tumors with the highest number of MC. In our hands, the trichoepithlioma had an increased proliferative activity but not an inereased number of MC. In basal cell carcinoma and trichofolliculoma MC were found in close proximity to proliferating tumor cells. Conclusion: Skin adnexal tumors of hair follicle differentiation often contain MC. MC seem to be involved in proliferation control. Though one might speculate about release of neuropeptides from MC to stimulate local growth the exact mechanism(s) by which the proliferation can be stimulated by MC remains to be elucidated.

        Key words: adnexal tumors of skin - hair follicle differentiation - Merkel cell - proliferative activity