Fewer than 45 children develop malignant germ cell tumours in the UK each year. Germ cell tumours can appear at any age. Germ cell tumours develop from cells that produce eggs or sperm. As a result, most germ cell tumours affect the ovaries or testes. However, it is possible for this type of tumour to develop in other parts of the body. During pregnancy, as a baby develops, the cells producing egg or sperm normally move to the ovaries or testes. However, occasionally they can settle in other parts of the body, where they can develop into tumours. The most common places for these tumours to occur are the area at the bottom of the spine (sacrococcygeal), the brain, chest and abdomen.
The tumours are sometimes given different names, depending on their characteristics, such as yolk-sac tumours, germinomas, embryonal carcinomas, teratomas and immature teratomas. They may be non-cancerous (benign) or cancerous (malignant). Malignant tumours have the ability to grow and spread to other parts of the body. Benign tumours do not spread, but may cause problems by pressing on nearby tissue and body structures. The behaviour of immature teratomas falls between benign and malignant; for example, they may spread within the abdomen, but not beyond this area, and can be removed surgically.