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Background:  p63, a member of the p53 gene family, is expressed in basal cells of several different organs.

Methods:  The immunoreactivity of p63 was examined in normal human epidermis and epidermal appendages and their tumors, and compared with proliferative activity as evaluated by Ki-67.

Results:  In normal skin, p63 expression was seen in basal/suprabasal cells of the epidermis, outer root sheath and hair matrix cells of the hair follicle, seboblast situated in the outermost layer of sebaceous glands, and outer layer cells of the ductal portion and myoepithelial cells of the secretory portion of the sweat glands. p63 expression was confined to the cells forming a continuous basal rim along the normal epithelial structure. In tumors, p63 expression resembled that in normal tissue in that tumor components originating from p63-positive cells were constantly positive for p63. In normal and tumor tissues, not all p63-positive cells were positive for Ki-67.

Conclusions:  p63 expression may be a marker of basal/progenitor cells in tumors of epidermis and epidermal appendages, and may be a diagnostic marker of these tumors.