Masciangelo R, et al. - In patients with borderline ovarian tumors (BOTs), authors assessed the safety of ovarian tissue transplantation. One of 11 BOT patients has BOT cells in frozen–thawed and xenografted ovarian tissue. Therefore preimplantation analysis is an absolute prerequisite. In cryopreserved ovarian tissue, endometriosis can also be detected, researchers suggest practicing caution in this scenario also.