Fertility preservation is now recognized as the most essential quality of life issue in young cancer survivors. Since the last decade several strategies to preserve fertility in women have been developed and applied clinically (although some are still experimental). Ovarian tissue cryobanking is currently perceived as a promising technology for fertility preservation which draws enormous attention not only from scientific communities but also from the general public. Ovarian tissue cryopreservation followed by transplantation has proven to be very successful not only in many animals but also in humans. Indeed, we have accumulated enough data since 2004 that ovarian transplantation can restore fertility in women. As of 2018, approximately 130 healthy babies have been born worldwide after transplantation of frozen-thawed ovarian tissue [1–9].

The first live birth to occur after ovarian-tissue transplantation between two genetically different sisters was reported in 2011. Since this is an acceptable practice with monozygotic twins, there is no apparent reason to refrain from using it with genetically different sisters, especially if one of the sisters previously received bone marrow from the other, leading to complete chimerism (HLA compatibility) between donor and recipient, thus obviating the need for immunosuppressive treatment. This approach allows for natural conception, which could be important on moral, ethical or religious grounds.