Stem cell theory for the pathogenesis of endometriosis.

Proposed hypothetical causes of endometriosis include retrograde menstruation, lymphatic and vascular metastasis, iatrogenic direct implantation, coelomic metaplasia, embryonic rest, and mesenchymal cell differentiation (induction). Each theory, individually, fails to account for all types of endometriotic lesions, thereby implicating combined and/or type-specific mechanisms. Recent evidence supports the presence of endometrial stem/progenitor cells and their possible involvement in eutopic endometrial regeneration and differentiation. Thus an additional novel mechanism for the origin of endometriotic lesions is that they arise from ectopic endometrial stem/progenitor cells.