Why screening for ovarian cancer may be important
Most ovarian cancers are diagnosed at an advanced stage, when they have already spread. Early stage ovarian cancer that is still confined to the ovaries has a much better outlook and can often be successfully treated. Unfortunately the disease is often not recognised in its early stages for a number of reasons.
First, cancer of the ovary usually develops after the menopause when the ovaries are inactive and abnormal function of the ovary is not readily noticed.
Second, the ovaries are located deep inside the pelvis and are inaccessible to examination.
Finally, even when symptoms do occur they are usually vague, non-specific symptoms which could be due to a host of other causes. For these reasons by the time most women with ovarian cancer develop significant symptoms and their cancer is diagnosed it has spread outside the ovaries to the pelvis (stage II), the abdomen (stage lll) or more distant sites (stage IV) and is far more difficult to treat successfully. This information suggests that an effective method of screening to detect early stage ovarian cancer may save the lives of many women who develop the cancer.
What screening tests are available?
Three potential methods of screening for ovarian cancer have been assessed:
1. Internal examination can be performed to identify enlarged ovaries. Although internal examination can detect large ovarian tumours even experienced doctors are not able to reliably detect ovarian cancer at an early stage. Internal examination is not regarded as an effective method for early detection of ovarian cancer.
2. CA 125 is a protein released into the blood in high levels in most women with ovarian cancer. The CA 125 blood test is frequently used to diagnose ovarian cancer in women who have symptoms and to monitor women after and during treatment of ovarian cancer. It is important to recognise that CA 125 is also produced by many normal tissues and levels in the bloodstream can therefore also be raised in normal situations (e.g. pregnancy, menstruation) and benign conditions as well as ovarian cancer. The CA 125 test is easily and quickly performed on a small blood sample sent to the laboratory.
3. Ultrasound scanning is the same technique as is used in pregnancy and can look at the size and texture of the ovaries. In ovarian cancer the ovaries increase in size and the texture becomes abnormal due to formation of cysts and solid growths. Unfortunately some of these abnormal features also occur in benign ovarian tumours and other conditions in the pelvis. So, as with CA 125, it is important to realise that ultrasound results can be abnormal even when there is no cancer present. Ultrasound scans can be performed either by placing a probe on the abdomen or by inserting a probe into the vagina.
How effective are the screening tests?
Screening can detect ovarian cancer at an early stage. Some large studies have looked at using either CA125 or ultrasound to screen for ovarian cancer. Two of the largest studies have been in the UK.
The King’s College Study investigated the role of ultrasound in over 5,000 women and demonstrated that it can detect ovarian cancer at an early stage. The Royal London and St Bartholomew’s Hospital Study assessed the use of CA 125 in combination with ultrasound in 22,000 women. This study revealed that it was possible to detect ovarian cancer before any symptoms developed.
It is still uncertain whether screening actually saves lives from ovarian cancer. Although screening with CA 125 and/or ultrasound can detect ovarian cancer early, it is important to be aware that this does not necessarily mean that screening will save lives. It is possible that even though screening detects cancer early it is not early enough to make a difference. Screening will only be worthwhile if it detects ovarian cancer sufficiently early to make treatment more effective.
What are the problems with screening for ovarian cancer?
False positive results are often found.
The major problem with screening for ovarian cancer is that both the CA 125 test and ultrasound scanning can be abnormal in women who do not have ovarian cancer. These sorts of results, known as false positives, are a serious problem as they can cause a great deal of anxiety. Even worse, if the abnormalities persist, it may ultimately be necessary to perform an operation to remove the ovaries and tubes in order to exclude the possibility of ovarian cancer which turns out to have been unnecessary. As ovarian cancer is relatively uncommon it works out that more abnormal screening results are due to false positive findings than are due to cancer.
False negative results can occur.
Most women find a normal screening result reassuring. However, it should be recognised that neither CA 125 or ultrasound will pick up every case of ovarian cancer. False negative results do occur and a small number of women will be falsely reassured.
What studies are in progress?
An ambitious study of ovarian cancer screening has been carried out in the UK. The study is called UKCTOCS (UK Collaborative Trial of Ovarian Cancer Screening) and involved 202,638 women aged 50-74 years from 13 regional centres. UKCTOCS is a randomised trial, which means that women who agreed to take part were randomly allocated to be screened with either CA 125 or ultrasound, or to a control group who were followed up without screening. This randomisation is essential in order to obtain clear answers about how effective ovarian cancer screening is at saving lives.
This study is now closed and results were published in 2015.These results are preliminary and there will be further data analysis for four years.
UKCTOCS is co-ordinated by the research team at the Gynaecological Cancer Research Centre at University College Hospital and is funded jointly by the Medical Research Council, Cancer Research UK and the Department of Health. Unlike previous screening studies, women did not volunteer to take part in UKCTOCS. Participation was by invitation from population registers to ensure that the results are representative of the whole population.
There is also a national study to assess and refine screening amongst women with a strong family history of ovarian cancer. This is the UK Familial Ovarian Cancer Screening Study (UKFOCSS). This study involved a CA125 blood test every four months and a yearly ultrasound scan. This study has now stopped taking on new volunteers.
Screening and you
Many women are concerned about their risk of developing ovarian cancer, particularly if they have a friend or relative who has developed the cancer. It is understandable that many women with this first-hand experience of ovarian cancer wish to be screened.
Women with a strong family history family history (two or more close relatives have had ovarian cancer, or one relative has had ovarian cancer and another has had breast cancer that occurred aged under 50) can ask their GP for a referral to a specialist genetics centre.
Women with a weak family history (one close relative who had ovarian cancer) may have a slightly increased risk and the value of screening is uncertain. However, the risk may be increased if they are from an Ashkenazi Jewish background. Some genetics centres do offer advice and counselling to women with a weak family history.
Women aged under 50 with no family history of ovarian or breast cancer are not at increased risk and the risk of false positive screening result is high. Screening is not recommended for women in this group.
Women aged over 50 with no family history of ovarian or breast cancer are not recommended to have routine screening as there is currently no evidence of its value to women in this group.
Last review April 2016
Date of next review April 2018