Background: Due to the remarkable improvement in treatments these last decades, long term survival can be expected in more than 80% of childhood cancer patients. Unfortunately, cancer treatments can be harmful to the gonads and can affect reproductive and endocrine functions. While loss of fertility is a major concern for most patients, sperm cryopreservation should be offered to all pubertal male patients. For prepubertal boys, only the experimental option of testicular biopsy in order to cryopreserve testicular stem cells can be proposed. Primary aims \- To cryopreserve testicular tissue of prepubertal patient receiving highly gonadotoxic oncological treatment. Secondary aims * To cryopreserve testicular tissue after failure of sperm cryopreservation in pubertal patient with high risk of infertility * To create a database in order to record clinical and biological follow-up data * To create a research biobank for future research projects Multicentric study: HUG, CHUV, UKBB