Cryopreservation of ovarian tissue: the biggest challenge of oncofertility.

Survival rates after cancer diagnosis and treatment have been raising through the last decades. Nowadays, oncofertility represents a useful strategy for young women affected by cancer to preserve their ovarian function and their family planning opportunity. Apart from more diffused techniques as cryopreservation of mature oocytes after controlled ovarian stimulation and gonadal downregulation with GnRH agonist depots, the cryopreservation of the cortical region of the ovarian tissue, which contains 90% of the follicular reserve, and later autologous transplant represent a possible and intriguing strategy. Nonetheless, the safety of the procedure is still a matter of debate and is a topic of great interest in both oncologic and reproductive fields. Especially, in order to improve the efficacy of the strategy the open questions are 1) how to search for malignant cells, 2) slow freezing vs. vitrification, 3) state of the art on the "artificial ovary". The aim of this review is to summarize the recent advances in ovarian tissue cryopreservation and present future perspectives.