PGR and endometriosis: Proinflammatory factors (like heme and iron) and cytokines (like tumor necrosis factor-alpha (TNFα) and interleukin 1 beta (IL1β)) may also disrupt PR function and play a role in progesterone resistance which finally leads to increased nuclear factor kappa B (NF-kB) activity, which is involved in endometriosis development [27,33,34].