We have changed our name from Cure Our Ovarian Cancer to the Ovarian Cancer Foundation NZ » Read More

high-grade serous ovarian cancer

High-grade serous ovarian cancer (HGSOC) is the most common type of ovarian cancer. About two-thirds of people diagnosed with ovarian cancer have high-grade serous ovarian cancer. It typically affects older women, with half being over 60 years of age at the time of diagnosis.

The grade of cancer describes how much cancer cells look like normal cells. High-grade cells grow quickly and look very different to normal cells under a microscope.


The symptoms of high-grade serous ovarian cancer are similar to other ovarian cancers and may include any of the following: bloating; eating less and feeling fuller; bowel habit changes; needing to pee more or urgently; abdominal, pelvic or back pain; and other symptoms. Symptoms that last four weeks or longer, particularly if they are unusual, frequent or worsening, should be investigated.

Diagnosis of high-grade serous ovarian cancer

High-grade serous ovarian cancer is an epithelial cancer. Epithelial tissues are widespread throughout the body. They form the covering of all body surfaces (like the outer surface of our skin and eyes), line body cavities and hollow organs, and are the major tissue in glands. ⁠

High-grade serous ovarian cancer is thought to mostly start in the epithelial cells of the fallopian tube before spreading to the ovary or, less commonly, to the peritoneum (lining of the abdomen). Most high-grade serous ovarian cancer is diagnosed when the cancer has spread.

Investigations for high-grade serous ovarian cancer usually include a pelvic examination, CA-125 blood test and imaging like a transvaginal ultrasound or CT. If ovarian cancer is suspected, a doctor specialising in the diagnosis of disease called a pathologist, will examine a sample of the tumour (usually taken during surgery) to confirm the diagnosis.

High-grade serous peritoneal cancer

High-grade serous peritoneal cancer is considered a variant of high-grade serous ovarian cancer. The peritoneum is the internal layer of the abdomen. In some people, high-grade serous cancer develops in the peritoneum instead of the ovary. The medical treatment for both conditions is the same.

Genetic risk factors

Approximately 1 in 5 people with high-grade serous ovarian cancer carry a mutation in the breast cancer (BRCA) 1 or 2 gene. Mutations in the BRCA gene are more common if people have a family history of ovarian cancer, breast cancer, prostate cancer and pancreatic cancer.

A genetic blood test can identify whether someone carries a germline BRCA mutation. A germline BRCA mutation can be found in all the cells in the body and may be inherited. If someone has the mutation, there is a 50% chance that siblings and children also carry the mutation.

If a BRCA mutation is identified before a cancer diagnosis, prophylactic surgery to remove the fallopian tubes and ovaries can almost eliminate the risk of developing ovarian cancer.

It is possible (but less common) to have a normal germline BRCA gene, but for a mutation to be found specifically in the cancer cells. This is called a somatic mutation and is not inheritable. In New Zealand, tumour testing for the BRCA mutation is available in some regions. Gynae-oncologists and oncologists can give more information about this process.

People with germline or somatic BRCA mutations may benefit from a type of targeted maintenance therapy called PARP inhibitors.


In New Zealand, treatment decisions are made in a multidisciplinary meeting. Doctors present individual cases to a group of specialists which includes gynae-oncologists, oncologists, pathologists and radiologists and together they decide what treatment should be offered.

Initial (frontline) treatment usually consists of surgery and/or chemotherapy. Chemotherapy may be administered through the veins (intravenous) or directly into the abdomen (intraperitoneal). Most people receive some form of carboplatin/paclitaxel chemotherapy.

Following chemotherapy, people may also be prescribed a PARP inhibitor as a maintenance treatment. In New Zealand, the PARP inhibitor olaparib (lynparza) is funded in newly diagnosed people following chemotherapy if they have a BRCA mutation in their germline (detectable via a blood test).

You can read more about the treatments for newly diagnosed high-grade serous carcinoma in the NCCN Ovarian Cancer Guidelines. The NCCN guidelines are an American resource and some treatments may differ in New Zealand.


Most (but not all) people with high-grade serous carcinoma will experience a recurrence or progression at some point. Recurrence is less likely when the cancer is found early.

If the cancer takes six months or longer to relapse following platinum-based chemotherapy (like carboplatin), it is said to be chemotherapy-sensitive or platinum-sensitive. If it takes less than six months to relapse it is considered platinum resistant.

If the cancer comes back or progresses, surgery and/or chemotherapy may be an option. Possible chemotherapy treatments include platinum-based carboplatin and non platinum-based chemotherapies such as paclitaxel, gemcitabine, doxorubicin and topotecan.

In New Zealand, the PARP inhibitor, olaparib (lynparza) is funded for maintenance in people following chemotherapy if they have a BRCA mutation in their germline and their high-grade serous ovarian cancer returns after initial treatment (if it was not provided as part of their initial treatment).

You can read more about the treatments for recurrent high-grade serous carcinoma in the NCCN Ovarian Cancer Guidelines. The NCCN guidelines are an American resource and some treatments may differ in New Zealand.

Unfunded treatments

Some ovarian cancer treatments available overseas in countries like Australia and the United Kingdom are not funded in New Zealand or may have additional restrictions as to their use. Some of these treatments are only used in recurrence overseas, while others are also used as part of front-line (initial) treatment.

Unfunded treatments include anti-vascular endothelial growth factor (VEGF) agents like bevacizumab (Avastin); PARP inhibitors like olaparib (lynparza), niraparib (Zejula) and rucaparib (Rubraca), Folate Receptor Antibody mirvetuximab soravtansine-gynx (Elahere); and chemotherapy agents like pegylated liposomal doxorubicin hydrochloride (Caelyx), in addition to different administration techniques like hyperthermic intraperitoneal chemotherapy (HIPEC), which is performed during surgery. 

Unfunded treatments can only be prescribed in the private healthcare system. Some life insurance policies and health insurance may pay a lump sum following a cancer diagnosis, to pay for unfunded treatments. Other people decide to undertake fundraising to pay for treatments.

Not everyone will benefit from an unfunded treatment but it is your right to be fully informed about your health decisions. If your doctor doesn’t mention unfunded treatments and you would like to know more, ask them.

Clinical trials

A clinical trial is research involving human participants. Clinical trials can offer new or different treatment options for people with ovarian cancer, and help doctors make better decisions for people in the future. Medications in a clinical trial are provided to participants at no cost. There may be unknown benefits and unique risks to participating in a clinical trial. An oncologist or gynae-oncologist can advise if there are any clinical trials which people may be eligible for.

As of October 2022, there are two clinical trials specifically for high-grade serous cancer patients currently recruiting in New Zealand.

  • The international study called ICON9 is comparing the efficacy, safety and tolerability of olaparib (a PARP inhibitor) with or without cediranib (an anti-VEGF agent) for maintenance in recurrent ovarian cancer. The trial is available in Christchurch and Auckland.
  • The international study called Keynote-B96 is comparing the effectiveness of pembrolizumab when used with paclitaxel, to paclitaxel without pembrolizumab for recurrent platinum-resistant epithelial ovarian cancer. The trial is available in Auckland. Pembrolizumab is a type of immunotherapy called a PD-1 inhibitor and is also known by the brand name Keytruda. Participants can also take bevacizumab in either trial arm if prescribed by their doctor (this may not be funded and is not a requirement to be part of the trial).

Find out more information about ovarian cancer.

Note: this content has been reviewed by a gynaecological cancer specialist in New Zealand. Information is provided for general use and should not be a substitute for professional medical advice.

Last reviewed: 16 January 2024