The differential expression of oestrogen receptors, progesterone receptors, Bcl-2 and Ki67 in endometrial polyps.

Objective: To obtain a greater understanding of the pathogenesis of endometrial polyps and to gain insight into which factors play a pivotal role in their growth.

Design: Retrospective analysis of archived paraffin-embedded specimens.

Setting: St James's University Hospital.

Sample: Thirty secretory phase endometrial samples, 10 secretory phase endometrial polyps, 8 proliferative phase endometrial samples and 10 proliferative phase endometrial polyps.

Methods: Immunohistochemistry was used to characterise the expression of oestrogen and progesterone receptors, Bcl-2 and Ki67 in cycling endometrium and phase-matched endometrial polyps. Patterns of expression were compared between the polyps and the endometrium.

Main Outcome Measure: The expression of oestrogen receptors, progesterone receptors, Bcl-2 and Ki67.

Results: Three significant differences were found between the endometrium and the polyps. Polyps taken from the proliferative phase of the cycle displayed significantly elevated expression of Bcl-2 and weak or no expression of progesterone receptors. Secretory phase polyps displayed an elevated expression of oestrogen receptors.

Conclusion: A localised increase in Bcl-2 expression and consequential decline or cessation of apoptosis is an important mechanism underlying the pathogenesis of endometrial polyps. Elevated Bcl-2 expression results in failure of the polyp tissue from undergoing normal cyclical apoptosis during the late secretory phase. This may mean the polyp is not shed along with the rest of the endometrium during menstruation.