The prognostic importance of nuclear morphometry and the MIB-1 index in rhabdomyosarcoma [corrected]

Both nuclear morphometry and an evaluation of the cell proliferative activity have been reported to be useful tools in predicting prognosis in malignant tumors. There have been few reports, however, on rhabdomyosarcoma regarding these evaluative techniques. We performed nuclear morphometry on 51 tumor specimens obtained either by biopsy or by resection of primary and untreated rhabdomyosarcomas, and we then evaluated MIB-1 staining on 25 of the 51 specimens. The morphometric analysis was semiautomatically performed on hematoxylin- and eosin-stained sections by using a personal computer. The areas, perimeters, and lengths of the major and minor axes of the best fitting ellipse of the nuclei were all measured. In addition, the Form Ell (nuclear ellipsoidity score: minor axis/major axis) was calculated. Using the monoclonal MIB-1 antibody, which detects Ki-67 antigen in formalin-fixed, paraffin-embedded tissue, immunohistochemical studies were performed. The values of the major and minor axes and the Form Ell showed significant differences between each histologic subtype whereas the values of nuclear areas did not. We defined the nucleus whose Form ELL was smaller than 0.25 as spindle-shaped nuclei and then divided all cases into two groups on the basis of the ratio of the spindle-shaped nuclei to the total number of nuclei of the tumor cells. The group with the higher ratio showed a significantly better prognosis (P < 0.05). The same trends were also found in the specimens with an embryonal subtype. Nuclear morphometry was a useful tool in predicting prognosis. In particular, the appearance of spindle tumor cells in rhabdomyosarcoma correlated with a better prognosis.