Morphometric index of adult renal cell carcinoma. Comparison with the Fuhrman grading system

Various grading systems have been proposed for renal cell carcinoma (RCC), using nuclear, cytoplasmic, and architectural features. The available evidence suggests that nuclear grading is a better prognostic indicator than other types of grading schemes. Nuclear morphometry may still improve the correlation of the nuclear grading with survival, however, because observer consistency is lacking in the subjective grading of RCC. The aim of this study was to investigate morphometrically whether RCC cases show a continuous spectrum of nuclear changes or whether there are discrete groups of cancer that correspond to the four Fuhrman grades. Karyometry was performed on 5- microm-thick, haematoxylin- and eosin-stained sections from 60 cases of conventional (clear cell) RCC. The analysis also included the evaluation of normal renal tissue (proximal tubules) adjacent to cancer. In each case the difference between the value of the cancer and the corresponding normal epithelium was calculated to represent, quantitatively, the degree of similarity between the tumour tissue and the internal normal control. When the differences were sorted into ascending order, a steady increase in values was observed for both the nuclear and the nucleolar features. A monotonic trend was evident for the differences in the mean maximum nuclear diameter and mean nucleolar area. When the differences between the values in the cancer and in the corresponding normal epithelium of these two features were summed up, the method resulted in a continuous variable, or nuclear morphometric index, related to the degree of deviation of each individual RCC from its internal normal control. The lowest index values were observed in of Fuhrman grade I cases, whereas values ranging from 2.679 to 5.422 were associated with cases graded II. Values equal to or higher than 5.951 were seen in the cases assigned to either grade III or grade IV. Partial overlap was present between the index values in grades III and IV. The RCC cases can be represented by a continuous index that corresponds to the morphological grading based on the Fuhrman scheme. This study shows that the index may be useful in supplementing the pathologist's grading. This issue can be further addressed with follow-up studies.