Expression of cyclin kinase inhibitor p27(Kip1) in skin tumours of dogs

Skin tumours (n = 14(.)8) of epidermal or hair follicle origin were examine d immunohistochemically to determine the expression of p27(Kip1) (p27), a c yclin-dependent kinase inhibitor (CDKI), and of Ki-67. In normal skin, a la rge number of basal cells of the epidermis and hair follicles were positive for Ki-67 and many suprabasal epithelial cells were positive for p27. Most of the hair matrix cells were positive for Ki-67 but negative for p27. Hai r papillae were strongly positive for p27. Squamous cell carcinomas had a p 27 positive index (PI) significantly lower than that of trichoepitheliomas (P <0(.)005), basal cell tumours (P <0(.)05) and intracutaneous cornifying epitheliomas (P <0(.)001). In contrast, Ki-67 PIs of squamous cell carcinom as and pilomatrixomas were significantly higher than those of trichoepithel iomas, basal cell tumours and intracutaneous cornifying epitheliomas (P <0( .)01 to P <0(.)001). No significant difference was observed between the Ki- 67 PI values of squamous cell carcinomas and pilomatrixomas. The results su ggested that p27 is capable of suppressing cell proliferation in the differ entiation of normal canine skin. In spite of being a benign neoplasm, pilom atrixomas had a low p27 expression; this may be a reflection of the prolife rative potential of the hair matrix. The expression of p27 may be a useful marker for the analysis of cell kinetics. (C) 2001 Harcourt Publishers Ltd.