Impact of Delayed Fixation on Evaluation of Cell Proliferation in Intracranial Malignant Tumors

Proliferative activity at tissue level, usually measured by mitotic count and immunohistochemical positive values by using anti-Ki-67 antibody, has been shown to be of prognostic significance in many tumors. However, the impact of delayed fixation on these parameters is not clear. Some studies reported a decrease in mitotic activity caused by delayed fixation, whereas others showed that the total number of mitotic figures remain unchanged. Most of these studies have been performed on experimental tumors; the only two reports that dealt with human cancer included a limited number of cases only. The aim of this study was to investigate the influence of delayed fixation on mitotic activity, evaluated with mitotic count (MC) and mitotic index (MI), and on Ki-67 labeling index in human neoplastic tissue. Twenty intracranial neoplasms were studied. These were fixed immediately after their removal and after a fixation delay of 3 and 12 hours, respectively. The mean value for the variation of the MC was 95% and 76% for 3 and 12 hours, respectively, of delayed fixation; the values for MI were similar: 91% and 73% for 3 and 12 hours, respectively, of delayed fixation. Ki-67 labeling index mean value was 90% both for 3 and 12 hours. All data were analyzed with the linear regression test, which demonstrated that high correspondence does exist between MC and MI and between MC and Ki-67 at the time of fixation (MC–MI, r = 0.93; MC–Ki-67, r = 0.59), but even after 12 hours of delay (MC–MI, r = 0.79; MC–Ki-67, r = 0.50); moreover the high correspondence was statistically significant at p < 0.05 both at the time of fixation and at 12 hours of delay. Our data seem to suggest that fixation delay does not affect cell proliferation.