Germ cell tumours start in the cells that form eggs within the ovaries. These types of tumours tend to develop in those who are younger, mostly under the age of 40. Less than 5 out of every 100 cases of ovarian cancer are germ cell ovarian cancer.  

There are many different subtypes of germ cell tumours. This means each subtype is quite rare. The different subtypes of germ cell tumours can behave and respond differently to treatment.  

Most germ cell ovarian cancer cases are diagnosed at an early stage. These early-stage tumours are often treated with surgery alone. Certain subtypes of germ cell cancers or more advanced tumours are treated with both surgery and chemotherapy.  

Germ cell tumours can be either non-cancerous (benign) or cancerous. The most common type of germ cell tumour is called a mature teratoma or dermoid cyst. These are usually non-cancerous. About 95 of 100 germ cell tumours are non-cancerous. 

Dysgerminoma

Dysgerminoma tumours most commonly affect those of reproductive age (from about age 15 to 45). It is the most common type of cancerous germ cell tumour. 

Teratoma

There are two main types of teratoma tumour – mature and immature.

Mature teratoma
Mature teratomas (or dermoid cysts) are the most common type of germ cell tumour. They are usually diagnosed between someone’s teenage years and their 40s. A dermoid cyst is normally present at birth but grows very slowly and so may not be noticeable until much later.  

Most of these cysts are non-cancerous (benign) and can be treated with surgery alone. The type of surgery you have will depend on your age, the size of the cyst and whether cancer is suspected. Your medical team will tell you about the options for your own situation. 

Immature teratoma
Immature ovarian teratomas are cancerous (malignant). They are usually diagnosed before someone’s early 20's. This type of cancer is rare. It is usually treated with a combination of surgery and chemotherapy. In most cases the affected ovary will need to be removed in surgery. But fertility is often kept if the other ovary and the womb aren’t removed.

Ovarian yolk sac tumour (OYST)

Ovarian yolk sac tumours (OYSTs) are a cancerous (malignant) germ cell tumour that are usually found in children and younger adults.

OYSTs are usually treated with surgery to remove the tumour, and chemotherapy. In those who are younger, it's sometimes possible to perform fertility-preserving surgery to keep the possibility of becoming pregnant in future. 

Mixed germ cell tumour (MGCT)

These ovarian tumours are made up of two or more types of germ cell tumours. They are cancerous (malignant).

Other types of germ cell ovarian tumours

There are other very rare types of germ cell tumours such as:

• Monodermal and highly specialised
• Embryonal carcinoma
• Choriocarcinoma  
• Germ cell sex cord stromal tumour