Detection of DNA strand breaks associated with apoptosis in human brain tumors

Apoptosis occurs spontaneously in a wide variety of neoplasms. However, it is difficult to detect apoptotic cells in routine histological sections because the cells undergoing apoptosis die singly and are then rapidly phagocytosed. Since DNA fragmentation is an important hallmark of apoptosis, visualization of DNA strand breaks in tissue sections provides the means for readily identifying apoptotic cells in situ. We have applied an in situ DNA strand break staining procedure for the quantitative estimation of apoptotic cells in surgical specimens of 62 different brain tumours. Positively stained apoptotic cells were observed in 25 (40.3%) cases and their percentage (apoptotic index) ranged from 0.1 to 8.9. Both fragmented and condensed nuclei of apoptotic cells and apoptotic bodies were stained. In addition, we assessed the proliferative activity of each specimen by immunostaining with the MIB-1 antibody (MIB-1 index) which detects the cell cycle phase-dependent Ki-67 antigen. Brain tumours with higher MIB-1 indices showed a tendency to higher apoptotic indices. The results of this study indicate that apoptosis occurs spontaneously in various brain tumours.