Immunohistochemical detection of Ki-67 in epithelial skin tumors in formalin-fixed paraffin-embedded tissue sections using a new monoclonal antibody (MIB-1).

The expression of the Ki-67 antigen was investigated in 44 epithelial skin tumors using an immunohistochemical technique on formalin-fixed, paraffin-embedded tissue sections. Microwave oven heating was employed for retrieval of the antigen in these tissue sections. The staining patterns varied among the epithelial skin tumors. The assessment of immunohistochemical staining was based upon the growth fraction (GF), defined as the number of Ki-67 positive cells divided by the total number of tumor cells counted and expressed as a percentage. GF was 9.7 +/- 3.1% in seborrheic keratosis, 19.5 +/- 2.9% in keratoacanthoma, 23.1 +/- 4.9% in basal cell carcinoma, 18.5 +/- 6.3% in actinic keratosis, 37.1 +/- 6.0% in Bowen's disease, and 32.9 +/- 10.5% in squamous cell carcinoma. There was a significant difference in GF between the keratoacanthoma and squamous cell carcinoma (p < 0.01). Actinic keratosis showed a relatively low GF, whereas Bowen's disease showed a high one. Furthermore, the GF tended to increase with tumor cell differentiation in squamous cell carcinoma: 23.7% (+/- 5.0) in well-differentiated, 35.0% (+/- 6.2) in moderately-differentiated, and 47.6% (+/- 4.5) in poorly-differentiated squamous cell carcinomas. Immunohistochemistry with MIB-1 may give useful additional information in the differential diagnosis of KA and SCC.