NGFR and endometriosis: The supporting evidence for endometriosis spread via the perineural approach is endometriotic lesions’ expression of nerve growth factor and the presence of the nerve growth factor (NGF) receptor (Trk-A) on the pelvic nerves [36]. Anaf et al. proposed that the expression of NGF in endometriosis and Trk-A on neural tissues results in the proliferation of the nerves that causes increased nerve sensitization and pain [36].