TUMOR-CELL PROLIFERATION AND APOPTOSIS IN MEDULLOBLASTOMA

The distribution of proliferating cell nuclear antigen (PCNA)-(clone P C 10)- and Ki-67- (clone MIB-1)-positive nuclei was investigated in 60 medulloblastomas of childhood. Although the labeling index of the two markers did not coincide, both showed a wide range of parallel variat ions. The percentage of positive nuclei was similar in both classic an d desmoplastic tumors. A variable proliferation capacity was found in the different tumor structures. Areas with neuronal and glial differen tiation showed very few positive nuclei; these were very abundant in t he infiltration areas, and along penetrating vessels from subarachnoid al growths. Pale islands were negative or positive only in their perip heral part. Large-cell areas were richer in positive nuclei than class ic ones, accounting for their more malignant character. Hyperchromatic round nuclei, not belonging to necrotic foci and called lymphocyte-li ke nuclei, differently interpreted in the past, were variably found in every case. They are known, from previous experience, to stain orange with Acridine Orange fluorochroming, like single-stranded DNA. They w ere not easily distinguishable from mitoses and were stained by in sit u end-labeling of DNA strand breaks, as demonstrated by incorporation of labeled nucleotides. They were regarded as possible apoptotic nucle i, representing either a peculiar type of cell death or the preservati on of the cell deletion capacity, typical of the embryonal tissue of o rigin.