With the advancement of assisted reproductive technology, more young cancer patients can consider having children. Ovaries and testes are important reproductive organs, and drugs, diseases, chemotherapy, and radiotherapy can all damage them. Reproductive preservation technology aims to protect patients whose reproductive ability has been damaged due to gonadotoxic drug therapy. Women can preserve their reproductive ability by freezing ovarian tissue cryopreservation so that they can have children in the future. Patients who have undergone or will undergo ovarian tissue cryopreservation in Hong Kong Children's Hospital will be invited to participate in the study. Here, we aim to evaluate the outcomes after ovarian tissue cryopreservation.

Inclusion Criteria:

• Patients aged from 0-18 years old and diagnosed with cancer
• Patients who have undergone or will undergo ovarian tissue cryopreservation in Hong Kong Children's Hospital
• For patients under 18 years old, parents/legal guardians will be asked to further sign the consent for them.

Exclusion Criteria:

• Patients unable to provide consent/assent (i.e. significant psychiatric problems/cognitive delay)
• Male patients

Patients who have undergone or will undergo ovarian tissue cryopreservation in the Hong Kong Children's Hospital will be invited to join this study.