**Abstract**

Endometriosis is a chronic inflammatory disease under hormonal/nonhormonal regulation, and microenvironment influences, originating in adult stem cells (mainly of bone marrow/endometrial progenitor mesenchymal type), and their exosomes, with special migratory and adhesion capacities. The postmenstrual repair with regeneration of eutopic and ectopic endometrium has similar genetic and epigenetic changes versus disease-free women. The competition between ectopic and eutopic endometrium for a limited supply of stem cells, and the depletion of normal stem cells flux to the uterus is considered the novel mechanism through which endometriosis interferes with endometrial functions and fertility. The gene expression DNA/RNA or microRNA changes/dysregulation of estrogen and progesterone receptors represent a possible explanation of progesterone resistance or loss of progesterone signalling in ectopic, and eutopic endometrium versus normal. The genes' changes involved in hormonal/non-hormonal pathways control of eutopic/ectopic endometrial cells, and of invaded tissues/organs may explain the disease persistency, progression and severity. Deficient DNA methylation of ERβ, the initial genomic event is followed by pathologic over-expressed ERβ in ectopic stromal cells, and it dictates the decline of PR isoforms, PRB being significantly lower in ectopic and eutopic endometrium. Altered expression of ERα, ERβ, and PRs accompanies the conversion of resident normal endometrial cells to ectopic lesions.

**Keywords:** endometriosis, progesterone resistance, stem cells, steroid receptors, genomic, epigenetics
