Stereological estimation of nuclear volume in benign and malignant melanocytic lesions of the skin. Inter- and intraobserver variability of malignancy grading.

The volume-weighted, mean nuclear volume (nuclear vv) may be estimated without any assumptions regarding nuclear shape using modern stereological techniques. As a part of an investigation concerning the prospects of nuclear vv for classification and malignancy grading of cutaneous melanocytic tumors, the observer variability of estimates of nuclear vv is studied. Routinely processed, paraffin embedded tissue specimens from 22 malignant melanomas and nine benign melanocytic cutaneous lesions are retrospectively investigated. The sampling scheme for estimation of nuclear vv is easy to use and robust, with more than 85% of the associated observed variance explained by differences among different tumors. Inter- and intraobserver reproducibilities are high, showing correlation coefficients of .86 and .96, respectively, with slopes of the regression lines close to unity. It is concluded that estimates of the three-dimensional nuclear vv in melanocytic cutaneous tumors are objective, unbiased, and highly reproducible.