Differential diagnosis of keratoacanthoma and squamous cell carcinoma of the epidermis by MIB-1 immunohistometry.

OBJECTIVE

For the analysis of cellular proliferative activity, the MIB-1 immunopositivity of keratoacanthoma (KA, n = 49), squamous cell carcinoma (SCC, n-48) and each of four cases diagnosed probably as KA or probably as SCC were analyzed by means of immunohistometry.

STUDY DESIGN

Immunohistochemical reactions were performed on 3-micron sections from routinely formalin-fixed and paraffin-embedded surgical specimens, using an indirect peroxidase method. The rate of immunostained cells was determined using a TV-image analysis system CM-2 (Hund, Germany). Twenty viewing fields (0.97 mm2) were measured with 20:1 objective magnification. An average of 1688 cells were assessed in each case.

RESULTS

The mean MIB-1 immunopositivity (MIB-1mean) was higher in SCC (42.3% +/- 19.1%) than in KA (26.8% +/- 9.8%). The distribution of the single values differed significantly (p = 0.0002). To test the suitability of MIB-1 immunohistometry for the differential diagnosis between KA and SCC, various thresholds were investigated. Using a threshold of 30%, SCC can be detected with a sensitivity of 70.8% (34 out of 48) and a specificity of 67.3% (33 out of 49). If a specificity of > or = 85% is required (42 out of 49, 85.7%), the sensitivity of the test decreases to 56.3% (27 out of 48) based on a threshold of 37.5%. Using the MIB-1 value of the most positive focus of the lesion (MIB-1max), the results were of minor significance; at a specificity level of > or = 85% (42 out of 49, 85.7%) a sensitivity rate of only 43.8% (21 out of 48) could be obtained (threshold: 75%).

CONCLUSION

As some overlap of the single values has to be considered, MIB-1 immunohistometry, although presenting new insights into the proliferative potential of KA and SCC, is of only limited value for the differential diagnosis of the two lesions in routine surgical pathology.