Epithelial ovarian cancer tumours start from the cells that line or cover the ovaries and fallopian tubes (the epithelium). There are many different subtypes of epithelial ovarian cancer. Treatment options can be different depending on the subtype of epithelial ovarian cancer.

High-grade serous

This is the most common form of epithelial ovarian cancer. It is sometimes called high-grade serous carcinoma. About 70 in every 100 cases of epithelial ovarian cancer are high-grade serous.  

Most high-grade serous ovarian cancers are now thought to start in the fallopian tube, not the ovary so they may be classified as fallopian tube cancer. Fallopian tube cancer is treated in the same way as ovarian cancer. The cancer cells can spread from the fallopian tube to the ovary.  

High-grade serous ovarian cancer is usually treated with a combination of chemotherapy and surgery. It generally responds well to chemotherapy. 

Low-grade serous

This is a relatively rare form of epithelial ovarian cancer. It is sometimes called low-grade serous carcinoma. About 5 in every 100 cases of ovarian cancer are low-grade serous. These tumours are usually slow growing and often affect those who are younger.  

Surgery is the most effective treatment for low-grade serous ovarian cancer. Chemotherapy and hormone therapies, such as Letrozole, are also used. Hormone therapies are drugs that work by reducing the amount of hormones in your body or by stopping them from reaching the cancer cells. These tumours respond less well to chemotherapy than high-grade serous tumours. 

Endometrioid

Endometrioid ovarian cancers make up about 10 in every 100 cases of epithelial ovarian cancer. It is usually treated with a mix of chemotherapy and surgery. They may be:

• endometriosis-associated, or developing from endometriosis. Endometriosis is a condition where cells like the ones that line your womb grow in other parts of the body.
• non-endometriosis-associated.

There's growing evidence that these may be two different types of ovarian cancer.  

In some cases of endometrioid ovarian cancer, there may also be a separate endometrial (womb) cancer or a condition called endometrial hyperplasia. This is a precancerous thickening of the lining of the womb.  

It's important to note that many more people have endometriosis than are diagnosed with ovarian cancer, so having endometriosis doesn’t mean you will develop ovarian cancer. 

Clear-cell

Clear cell ovarian tumours are a rare type of ovarian cancer and make up about 10 in every 100 cases of epithelial ovarian cancer. They are also known as clear cell carcinoma (CCC). This type of ovarian cancer is sometimes linked to endometriosis.

Clear cell ovarian cancer is treated in the same way as other epithelial ovarian cancers with a combination of surgery and chemotherapy. They respond less well to chemotherapy. 

Mucinous

Mucinous tumours are rare and make up about 3 in every 100 cases of epithelial ovarian cancer. This type of ovarian cancer is usually treated with surgery with or without chemotherapy, but doesn’t respond as well to chemotherapy as other epithelial ovarian cancers.

Mucinous tumours include:  

• primary mucinous ovarian cancer. In these cases, the tumours start in the ovary.
• metastatic, from other sites. In these cases, the cancer cells have spread from somewhere else in the body, most often from the bowels or stomach. It wouldn’t be classified as ovarian cancer since it did not start from cells in the ovaries.  

Other tests are often needed in order to know whether a mucinous ovarian tumour is ovarian cancer or if it is metastatic and has come from another part of the body. A colonoscopy or gastroscopy is used to rule out whether the cancer started outside of the ovaries. This is when a small camera is inserted into the back passage (bottom) or the stomach. 

Undifferentiated or unclassified 

Some epithelial ovarian cancers are known as unclassified or undifferentiated. This is because the tumour cells are very underdeveloped (undifferentiated) and it's not possible to tell what type of ovarian cells they started to grow from. These are usually treated with a combination of surgery and chemotherapy.

Brenner tumours

Brenner tumours are rare, making up 1 or 2 in every 100 cases of ovarian cancer. Surgery is the most common form of treatment for these tumours.  

Brenner tumours can be non-cancerous (benign), slow growing (borderline) or cancerous (malignant). Most Brenner tumours are non-cancerous. Less than 5 in 100 Brenner tumours are slow growing or cancerous. 

Borderline tumours

Borderline tumours are rarer than cancerous ovarian tumours. They usually grow very slowly and are less likely to spread to other parts of the body. Borderline tumours are also known as tumours of low malignant potential. In borderline tumours, the cells look different to healthy cells but they are not considered cancerous.  

Borderline tumours are staged using the same FIGO system as ovarian cancers. They're usually treated by surgery alone.  

There are subtypes of borderline tumours, depending on what type of cells they are made up of, including:

• serous
• mucinous
• and, more rarely, clear cell or endometrioid. 

Ovarian carcinosarcoma

Ovarian carcinosarcomas are rare. They contain cells that look like both:

• high-grade epithelial ovarian cancer and  
• connective tissue cancer (a sarcoma). Connective tissue is tissue that supports, connects or separates different parts of your body, such as cartilage or tendons.  

Ovarian carcinosarcomas behave like high-grade epithelial cancers and are treated in the same way with chemotherapy and surgery.

Primary peritoneal cancer 

Primary peritoneal cancer (PPC) is similar to epithelial ovarian and fallopian tube cancer. It’s usually classed and treated in the same way. Unlike ovarian cancer, PPC doesn’t start in the ovaries but in the peritoneum. 

The peritoneum is a large, thin, flexible sheet of transparent tissue that covers the organs inside your tummy including your bowels, stomach, liver and reproductive organs. This means even those who have had their ovaries removed can develop this type of ovarian cancer.