Atypical mitoses with rod and dot-shaped extra pieces of chromosomes separate to the main spindle are commonly seen in HPV-associated intraepithelial lesions. To determine the reproducibility and correlation of HPV-associated atypical mitoses (HAM) with histological diagnosis and p16 status, we performed a retrospective study.
A total of 100 consecutive cervical biopsies, 10 vulvar HSIL (usual VIN), 10 differentiated VIN, 10 vulvar condylomata, 5 normal proliferative endometrial, and 5 normal ovarian follicles were assessed. The first 10 mitoses were examined in the cervical biopsies, and the case recorded as positive when one HAM was identified. The first 50 mitoses in the vulvar cases and controls were examined, and the percentage of HAM was calculated.
HAM were found in 62.5% of HSIL, 14.7% of LSIL, and 0% of benign cervical biopsies. When p16 was positive, 62.7% showed HAM, and when p16 was negative, 12.5% showed HAM. HAM were commonly found in vulvar HSIL, 12% of all mitoses, but extra dots of chromosome were also occasionally found in the mitoses of differentiated VIN (1%) and rarely in normal controls (0.2%). No HAM were found in condylomata.
HAM was useful to confirm SIL, but the incidence was too low for absence to exclude SIL. Although HAM are more common in HSIL, they cannot be relied upon to distinguish HSIL from LSIL. The dot form of HAM is less reliable than the rod form, as extra dots of chromosomes may be occasionally seen in differentiated VIN and rarely seen in normal proliferative endometrium.