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, only the experimental option of ovarian tissue cryopreservation can be proposed to prepubertal girls with a high risk of infertility. For pubertal patient, cryopreservation of mature oocytes after ovarian stimulation can be offered if oncological treatment debut can be delayed. As it is often not possible, ovarian tissue cryopreservation can also be offered. Primary aims \- To cryopreserve ovarian tissue of pre or peripubertal patient who will be receiving highly gonadotoxic oncological treatment. Secondary aims * To create a database in order to record clinical and biological follow-up data * To pool resources with Fertisave Registry * To create a research biobank for future research projects Multicentric study: HUG, CHUV