Atypical mitotic figures and the mitotic index in cervical intraepithelial neoplasia

We surveyed cervical intraepithelial neoplasia (CIN) to quantify the proliferation rate and the presence of normal and atypical mitotic figures. In the cervical tissue specimens of 127 women with CIN, the area with the highest cell proliferation was identified and, at that site, the proliferation rate was assessed by calculating the mitotic index (MI). Lesions with an MI <2 were not considered further. In the area with the highest proliferation rate, 228 mitoses were classified into one of the following groups: normal mitotic figures (NMFs), lag-type mitoses (LTMs) comprising three group metaphases (3GMs), two group metaphases (2GMs) and other lag-type mitoses (OLTMs), multipolar mitoses (MPMs) comprising tripolar mitoses (3PMs) and quadripolar mitoses (4PMs), and other atypical mitotic figures (OAMFs). The median value of the MI increased significantly from 3 in CIN I through 4 in CIN II to 9 in CIN III (P<0.001). The occurrence of the different LTMs was mutually correlated. The frequency of LTMs increased significantly with increasing CIN grade (P<0.001), whereas the frequency of NMFs decreased significantly with increasing CIN grade (P<0.001). The frequency of OAMFs was not related to CIN grade (P=0.94). MPMs were present in low numbers in a minority of the lesions. Spearman's rank correlation coefficient (with 95% confidence limits) between the MI and the number of LTMs, OAMFs and NMFs was 0.66 (0.53; 0.75), –0.14 (–0.32; 0.05) and –0.51 (–0.63; –0.35), respectively. Increasing CIN grade is associated with increasing MI, increasing numbers of LTMs, and decreasing numbers of NMFs. MPMs are very rare events in CIN. The abundant presence of OAMFs seems to be independent of CIN grade and MI.