Simple hyperplasia of the endometrium: An evaluation of proliferative activity by Ki-67 immunostaining

As endometrial hyperplasia has been characterized over the past 100 years, some investigators have questioned the hyperplastic nature of nonatrophic c ystic glands associated with an increase in gland-to-stroma ratio, which is currently considered to represent simple endometrial hyperplasia. In the c urrent study, the proliferative activity of simple endometrial hyperplasia was examined using an antibody to Ki-67 protein, a well-established marker of proliferative activity, and compared with the results of activity in ina ctive/atrophic endometrium, proliferative endometrium, and other forms of e ndometrial hyperplasia. In an evaluation of 68 endometrial biopsy specimens showing 110 histologic patterns, the mean Ki-67 index (percentage of Ki-67 positive nuclei) was 2.8% in inactive/atrophic endometrium, 23.2% in proli ferative endometrium, 9.8% in simple hyperplasia, 12.7% in complex hyperpla sia, and 10% in atypical complex hyperplasia. In simple hyperplasias, the m ean Ki-67 index was 3.9% in dilated glands without infolding or outbranchin g, 14.6% in nondilated glands showing outbranching or plight crowding, and 6.9% in dilated glands with infolding or outbranching. Ki-67 indices for di lated glands were most similar, therefore, to atrophic/inactive endometrium with no statistical significant difference in the percentage of these cell s staining between these two groups. In contrast, statistically significant differences were seen in staining between cystic patterns of simple hyperp lasia and proliferative endometrium, simple hyperplasia showing outbranchin g and/or slight crowding but no dilation, complex hyperplasia, and atypical hyperplasia. The findings in the current study suggest that nonatrophic cy stic glands with an increase in the gland-to-stroma ratio in the endometriu m should not he considered a hyperplastic process and in the absence of oth er Findings such as excessive bleeding or coexistent noncystic simple hyper plasia, treatment with progestin therapy, a widely used practice, is unnece ssary. As discussed, the findings also suggest that these cystic forms of s imple hyperplasia are precursors of cystic atrophies. Confirmation of these results on a larger population by a different research team appears desira ble.