Spermatogonial stem cells (SSCs) enable continuous sperm production for almost the entire life of a male. Spermatogonial transplantation (SGT) was a revolutionary technique in the study of male germ-cell biology. Semen cryopreservation of young male cancer patients is becoming common in clinical practice. SSCs can be obtained from small fragmental testis tissues of pediatric cancer patients, taken by a biopsy procedure. The SSCs could be cryopreserved for later use, if patients survive the disease and grow to reproductive age. Most importantly, in vitro spermatogenesis circumvents the invasive procedure of cell transplantation, let alone the possible reintroduction of malignant cells to the patient when SSCs are cryopreserved. In vitro human spermatogenesis, just after the development of mouse in vitro spermatogenesis, might be a focus for research interest. It may not be easy to achieve. In particular, the duration of spermatogenesis is longer in humans (64 days) than in mice (35 days).

Loss of fertility in adult life is a major psychologically traumatic consequence of cancer treatment. Improving therapeutic regimens using less gonadotoxic protocols could enable spontaneous recovery of spermatogenesis, but their use is not always possible without compromising patient survival. Cryopreservation of testicular tissue pieces may be considered as an alternative method capable of maintaining cell-to-cell contacts between Sertoli and germinal stem cells, and therefore preserving the stem cell niche necessary for their survival and subsequent maturation. In humans, preclinical in vitro studies using cadaver or surgically removed testes have demonstrated the feasibility of transplanting germ cell suspensions into testes. The first convincing demonstration of human testis transplantation was reported in 1978. The most important, life-threatening concern of spermatogonial transplantation is the risk of reintroducing malignant cells. Providing young people undergoing gonadotoxic treatment with adequate fertility preservation strategies is a challenging area of reproductive medicine.