Proliferation in Postmenopausal Endometrial Polyps-A Potential for Malignant Transformation

Abstract

Background and objectives: Endometrial polyps in asymptomatic postmenopausal women are often incidentally found, yet only 1.51% of them are malignant. Their potential for malignant transformation has not been adequately addressed. The aim of this study was to investigate the proliferation within endometrial polyps as one of the indicators of their malignization potential in asymptomatic postmenopausal women. Materials and Methods: Immunohistochemical studies of Ki-67 were performed. Cases included 52 benign postmenopausal polyps, 19 endometrioid carcinoma with coexisting benign polyps, 12 polyps with foci of carcinoma and 4 cases of polyps, which later developed carcinoma. The control group included 31 atrophic endometria and 32 benign premenopausal polyps. Ki-67 was scored in either 10 or 20 "hot spot" fields, as percentage of positively stained cells. Results: The median epithelial Ki-67 score in postmenopausal benign polyps (4.7%) was significantly higher than in atrophic endometria (2.41%, p < 0.0001) and significantly lower than in premenopausal benign polyps (11.4%, p = 0.003) and endometrial cancer (8.3%, p < 0.0001). Where endometrial polyps were found in association with endometrial carcinoma, Ki-67 was significantly higher in cancer (p < 0.0001). No significant difference was found between Ki-67 scores of cancer focus and of the polyps tissue itself, respectively 2.8% and 4.55%, p = 0.37. Ki-67 expression, where polyps were resected and women later developed cancer, was not significantly different (p = 0.199). Conclusion: Polyps from asymptomatic postmenopausal women showed significantly more proliferation in both epithelial and stromal components than inactive atrophic endometria but less than premenopausal benign polyps and/or endometrial cancer. Benign postmenopausal endometrial polyps exhibit low proliferative activity, suggesting low malignant potential and may not require resection in asymptomatic women.

Keywords: Ki-67; endometrial polyps; malignancy; postmenopausal; proliferation.

Figure 1

(A) A case of postmenopausal benign polyp. (B) A case of premenopausal benign polyp. (C) A case of atrophic endometrium. (D) A case of endometrial cancer. Original magnification 40× (A–D).

Figure 2

Box and whisker plots showing epithelial (a) and stromal (b) expression of Ki-67 over the spectrum of endometrial lesions. Boxes extend from the 25th to 75th percentiles and whiskers mark the range. Medians are displayed as horizontal lines within the boxes. The circles and asterisks represent points more than 1.5 IQR (interquartile range) and 3 IQR from the nearer quartile, respectively. Abbreviations: PostM EP, postmenopausal benign endometrial polyps. PremM EP, premenopausal benign endometrial polyps. EC, endometrial cancer. Malignant EP, endometrial polyps including polyp tissue of cases where polyp was found with coexisting endometrial cancer or had carcinoma focus inside.

Figure 3

Box and whisker plot showing epithelial expression of Ki-67 over the spectrum of endometrial lesions in selected cases. Boxes extend from the 25th to 75th percentiles and whiskers mark the range. Medians are displayed as horizontal lines within the boxes. The circles and asterisks represent points more than 1.5 IQR and 3 IQR from the nearer quartile, respectively. *, p < 0.05. Abbreviations: PostM, postmenopausal polyps. EP, endometrial polyp. EC, endometrial carcinoma. a—cases of endometrial carcinoma with coexisting benign endometrial polyps; b—cases of endometrial polyps with foci of endometrial carcinoma; c—cases of endometrial polyps and later developed endometrial carcinoma.

Figure 4

Comparison of Ki-67 scores according to staging (a) and histodifferentation (b). Boxes extend from 25th to 75th percentiles and whiskers mark the range. Medians are displayed as horizontal lines within the boxes. The circles are points more than 1.5 IQR from the nearer quartile. Abbreviations: FIGO, The International Federation of Gynaecology and Obstetrics.

Figure 5

Immunohistochemical staining with Ki-67 in different grades of histodifferentation. G1: high differentiation degree. G2: moderate differentiation degree. G3: poor differentiation degree.