IGF1 and endometriosis: In addition, using an in vitro endometriosis model, we found that the synthetic Ec peptide of the IGF-1Ec isoform stimulated the growth of KLE endometrial-like cells, suggesting that the IGF-1Ec isoform might generate, apart from the IGF-1 receptor-mediated bioactive mature IGF-1 peptide, another post-translational bioactive product that may have an important role in endometriosis pathophysiology [33].