Ovarian cancer is made up of more than one disease.
It's often spoken about as one disease - cancer of the ovaries – but there are actually different types of ovarian cancer – classified by where the cancerous cells first began to grow.
There are three main types of ovarian tumour. If you’re diagnosed with ovarian cancer, your doctor will tell you what type of tumour you have.
The three types of ovarian tumour are:
Epithelial ovarian cancer is the most common type of ovarian cancer, accounting for 90% of all cases.
An epithelial ovarian tumour develops on the surface of the ovary. Some are benign, but some are malignant. There are six types of epithelial ovarian tumour:
- Serous tumours
These occur most often in women between the ages of 40 and 60. They are the most common type of epithelial tumour, representing up to 40% of cases. Sometimes they’re cancerous, sometimes they’re not: 50% are malignant (cancerous), 33% are benign (non-cancerous), and 17% are mildly cancerous, meaning the tumour grows very slowly.
- Endometrioid tumours
These occur primarily in women aged 50 to 70. Around 20% of epithelial tumours are endometrioid tumours and most are malignant. About 20% of endometrioid tumours occur in women who also have endometrial carcinoma and 5% are linked to endometriosis, a disorder of the lining of the womb.
- Clear cell tumours
These occur primarily in women aged 40 to 80. They make up 6% of epithelial tumours and are almost always malignant. About 50% are associated with endometriosis.
- Mucinous tumours
These tumours are most common in women aged 30 to 50 and make up roughly 10% of epithelial tumours. Most of the time they’re not cancerous: 75% of mucinous tumours are benign, 15% are malignant, and 10% are on the borderline.
- Undifferentiated tumours
These do not fit neatly into any category and account for about 15% of epithelial tumours. They tend to be malignant.
- Transitional cell tumours
These are mostly malignant tumours and are often made up of cells that look like the cells that line the urinary tract.
Germ cell tumours originate in the cells within the ovary that develop into eggs. These types of tumours account for 5-10% of ovarian cancer cases and they tend to occur in younger women (mostly in their 20s). Most germ cell tumours are non-cancerous and 90% of cases can be successfully treated.
Sex cord stromal tumours begin in the connective cells that hold the ovaries together. They can affect all age groups. Most of these tumours are either not cancerous or are very slow growing and account for 5% of all ovarian cancer cases.
Primary peritoneal carcinoma
Primary peritoneal carcinoma is not a type of ovarian cancer but it is closely related to epithelial ovarian cancer. It’s also sometimes referred to as extra-ovarian primary peritoneal carcinoma or serious surface papillary carcinoma.
This type of cancer is rare and develops from the cells that line the pelvis. It has the same symptoms as ovarian cancer and is diagnosed and treated in the same way.