"Runt-related transcription factor 1 (RUNX1) is a transcription factor that has previously been identified as a regulator in securing the identity of ovarian-supporting cells and the ovary. Considering its role in ovarian development, we set up to investigate how changes in the expression of the gene RUNX1 are linked to ovarian dysfunction. We first focused on the effects of the loss of Runx1 in the mouse ovary by generating a conditional knockout (KO) of Runx1 where the gene was removed in somatic cells expressing Steroidogenic factor 1 (SF1). We collected ovaries at 4.5- and 15-months and characterized their phenotypes using histology, immunostaining, and gene expression analyses. The results at the 4.5 months revealed the occurrence of abnormal, asymmetrical ovarian follicles in the Runx1 KO mice. These abnormal follicles lacked signs of cell proliferation or apoptosis, suggesting that these follicles remain quiescent at this time. Several genes previously demonstrated to be involved in tumor progression are altered in Runx1 KO mice. RNA-Sequencing analysis led to the identification of differentially expressed genes in Runx1 KO ovaries, including genes involved in ovarian cancer. At 15 months of age, about one fourth of Runx1 KO mice developed ovarian masses. We are currently examining the molecular pathways that are affected by the loss of RUNX1 and developing the Runx1 overexpression model. Understanding how certain genes play a role in cancer will enhance our ability to overcome the challenges of early detection, develop therapeutic strategies and help in improving the survival of the patients."