Early-stage endometriosis: adhesion and growth of human menstrual endometrium in nude mice.

Objective: To evaluate the implantation of menstrual endometrium and the early stages of evolution of endometriotic lesions.

Design: Experimental prospective study.

Setting: An academic research environment.

Animals: Ten nude mice.

Intervention(s): A minilaparotomy was performed to place fresh human menstrual endometrial samples in the peritoneal cavity. Removal of the transplants was performed successively on days 1, 3, and 5 by laparotomy.

Main Outcome Measure(s): Adhesion of endometrial fragments and early stages of endometrial lesions was morphologically and immunohistochemically studied.

Result(s): As early as day 1, stromal cells were found to be attached to the mesothelium. A progressive reorganization of epithelial and stromal cells into endometrial glands was observed. On day 5, cystic endometriotic lesions were characterized by more extensive proliferative activity in glandular cells and a higher VEGF score in stromal cells than that observed in previously removed transplants.

Conclusion(s): Menstrual human endometrium is able to implant on intact mesothelium and to reorganize itself into structured glands and stroma under the influence of unknown factors. We suggest that stromal and glandular cells have two distinct roles: stromal cells are involved in the attachment process and glandular cells in the growth of the endometriotic lesion.