Ovarian tissue cryopreservation in young cancer patients for fertility preservation.

Several options are currently available to preserve fertility and give female cancer survivors a chance to have children at a later date, including the cryopreservation of embryos, oocytes, and ovarian tissue. Selection of the most suitable strategy to preserve fertility depends on the type and timing of anticancer therapy, the cancer, the patient's age, and the presence of the patient's partner. Several studies have shown that the ovarian tissue can be successfully frozen and later grafted in the human womb. To date, approximately 30 live births have been achieved after the transplantation of frozen-thawed ovarian tissue. At present, the standard procedure for cryopreservation of ovarian tissue is the slow-cooling method. The slow-cooling method uses an optimal cooling rate for the target cells, and relies on extracellular ice crystals to gradually dehydrate and equilibrate the tissue. Several groups reported that slow cooling is more efficient than vitrification for the cryopreservation of human ovarian tissue. However, vitrification can be performed under a variety of conditions, and therefore, the choice of methods is important. In addition, vitrification traps aqueous solutions in an amorphous, "vitreous" solid phase that prevents ice crystal formation in tissues. Vitrification methods that were developed using mice and monkey have recently been shown to improve the viability of vitrified ovarian tissues. In this review article, recent topics of ovarian tissue cryopreservation are described.