Ovarian cancer is the fifth most common cancer in women, after breast, lung, bowel and endometrial (womb lining) cancers. Each year approximately 7,000 women in the UK are diagnosed with the disease. Around 10% of ovarian cancers are due to inherited genetic factors but the majority occur in women without a family history of the disease.
There are different categories of ovarian cancer:
The most common ovarian cancer is epithelial ovarian cancer. This occurs mainly in postmenopausal women and accounts for about 90% of cases. It affects the surface layers of the ovary and there are different types of this cancer.
- high grade serous – the commonest and one of the most dangerous types. Also the type most commonly found in women with a family history of the disease. Around one in 10 cases of this type of cancer are due to an inherited predisposition.
- endometrioid – less common than high grade serous, and generally has a better prognosis, possibly because it tends to be detected before it has spread as far. The risk of this type of cancer is slightly increased in women with endometriosis (a common condition where cells from the lining of the womb are found at other sites where they would not normally be found, such as on the surface of the ovary). However, the vast majority of women with endometriosis do not develop ovarian cancer.
- clear cell – a relatively uncommon type of ovarian cancer, which usually has a better prognosis than high grade serous cancer because it is often diagnosed before it has spread. The risk of this type of cancer is also increased slightly in women with endometriosis.
- mucinous cancer – this type is unusual and when it is found it is important to exclude the possibility that the cancer started at another site such as the bowel. It tends to be detected before it has spread and so it generally has a better prognosis than high grade serous cancer.
- undifferentiated cancer – this type is relatively rare and has a poor prognosis. Undifferentiated is a description of the appearance of the cells through the microscope.
- borderline tumours – these are not true cancers, but contain cells which resemble cancer cells. They are generally slow growing and rarely invade into other organs, even when they have spread, so they usually have an excellent prognosis.
1-2% of ovarian cancers are germ cell tumours, which start in the cells that become the eggs in the ovary. These rare tumours tend to occur in younger women (most commonly in their 20s) and usually have a very good prognosis.
These are rare types of ovarian cancer and can cause strange symptoms as they sometimes produce excess hormones. For example, too much oestrogen may cause abnormal vaginal bleeding and too much testosterone may cause abnormal hair growth or a deeper voice.
Ovarian cancer is ‘staged’ according to how far it has spread at the time it is diagnosed. This is normally determined by a staging operation:
- Stage 1 – the cancer is confined to the ovaries
- Stage 2 – the cancer has spread to other structures within the pelvis (for example the womb or fallopian tubes), but has not spread to the abdomen
- Stage 3 – the cancer has spread within the abdomen or is present in lymph glands in the pelvis or abdomen
- Stage 4 – the cancer has spread outside the abdomen (for example into the chest in the space surrounding the lungs)
The higher the stage, the further the ovarian cancer has spread. This affects prognosis; usually the prognosis of lower or ‘early stage’ cancers is better than that of the higher or ‘advanced’ stage cancers.
For most women with a family history of the disease, their risk of ovarian cancer will not be much higher than that of the general public (around one in seventy women get ovarian cancer in their lifetime).
If you have a first-degree relative with ovarian cancer (mother, sister or daughter), then your risk may be increased to around one in twenty. This is considered to be moderately increased risk.
However, if there are two or more relatives with ovarian cancer in your family, or one relative with ovarian cancer and one with breast cancer before the age of 50 yr (or two relatives with breast cancer before the age of 60 yr), then you may be at high risk of developing ovarian cancer. In certain cases, this risk could be as high as one in two by age 70 yr.
If there is Ashkenazi (Eastern European) Jewish ancestry on the same side of your family as a relative with ovarian cancer, then there could be an inherited predisposition to cancer in your family, even if only one relative has had the disease.
A family history of ovarian cancer could raise the possibility of a BRCA1 or BRCA2 gene alteration being present in the family. This is especially true if there is also a history of breast cancer or Ashkenazi Jewish ancestry on the same side of the family. More recently, it has also become apparent that around 1 in 10 women with the commonest type of ovarian cancer (high grade serous cancer) carry one of these gene alterations.
If there is a strong family history of bowel and/or endometrial (womb-lining) cancer, then this should raise the possibility of a different inherited predisposition to cancer, known as Lynch Syndrome. Women with this condition also have an increased risk of ovarian cancer.
Does anything apart from my family history affect my risk of ovarian cancer?
We know that the following can affect the risk, but none of these factors influence risk as much as a strong family history of the disease:
- Using the combined oral contraceptive pill halves your risk if you have used it for 5 years or more
- Using other types of hormonal contraception (minipill, injectable contraception, contraceptive implants) can reduce your risk of ovarian cancer
- Breastfeeding reduces the risk of ovarian cancer
- The more children you have had, the lower your risk of ovarian cancer
- Having a sterilisation operation (clips placed on the Fallopian tubes) reduces the risk of ovarian cancer
- Taking hormone replacement therapy (HRT), having endometriosis, being overweight or smoking all slightly increase the risk of ovarian cancer
- Using talc on the genital area may cause a small increase in risk
- Exposure to asbestos may cause a small increase in risk
- Some fertility treatments may cause a slight increase in risk, but this risk is small and probably confined to women who do not achieve a successful pregnancy following fertility treatment. Also, fertility treatment probably only increases the risk of borderline ovarian tumours which tend to have a very good prognosis
- Recent evidence has suggested that premenopausal women with polycystic ovarian syndrome may have a slightly higher risk of ovarian cancer