This is a pilot clinical trial to evaluate the feasibility and outcome of autologous transplantation of immature testicular tissue cryopreserved during childhood as a method of fertility preservation for prepubertal boys in case of gonadotoxic therapies.

Freezing of immature testicular tissue is performed since the early 2000s and a number of our patients have now reached reproductive age. In case of childwish and azoospermia in adulthood, surgical sperm retrieval is planned and if unsucessful transplantation of the patient's own cryopreserved tissue will be performed during the same surgical intervention as a fertility restoration method.

Inclusion Criteria: all are required

• patients who have completed their gonadotoxic treatment
• patients who are in good health after care of the primary disease based on hemato-oncologist input
• patients with proven azoospermia in adulthood and child's wish requesting transplantation
• patients who cryopreserved and stored their immature testicular tissue (in conformity with regulatory requirements)
• in case of prior hematological malignant disease or metatstatic cancer, if the multidisciplinary assesment considers the risk of cancer cell contamination is negligible

Exclusion Criteria:

• patients for whom the cryostored tissue presents a non-negligible risk of cancer cells contamination
• patients presenting with a contraindication for general anethesia

Male adult survivors of a childhood cancer who cryopreserved their tissue for own use as a fertility preservation method are eligible.