Question: A friend died of ovarian cancer. By the time it was discovered, it was too late to cure her. I recently read that American doctors are developing a new test to look for ovarian cancer. When will this test be available for the public?
Answer: What happened to your friend is, unfortunately, fairly common with ovarian cancer. About 75 per cent of cases are diagnosed when the cancer is well advanced and difficult to treat. Most patients don’t have any obvious signs of the disease in the early stages. Later on, they may experience rather vague abdominal symptoms such as bloating, indigestion, pelvic discomfort, constipation or diarrhea that can persist for months.
These symptoms are often mistaken for stomach troubles and not immediately linked to a cancer that starts in the cells of the ovaries – the pair of almond-sized organs that lie on opposite sides of the uterus or womb. (The ovaries – part of the female reproductive system – produce eggs, plus the hormones estrogen and progesterone.)
Scientists have been trying to develop a simple blood test that can help catch the cancer when it is just starting to grow. In fact, about three decades ago, researchers identified a protein, called CA-125, which is produced by ovarian tumors and ends up in the bloodstream. But the protein can also become elevated by other ailments such as uterine fibroids. That means the test can lead to a “false positive” – essentially a false alarm. In earlier studies using this test, women have had surgery to remove a mass that turned out to be a relatively harmless cyst.
Now, however, some researchers think they can reduce false positives by using a unique algorithm, or mathematical calculation, to analysis changes in CA-125 levels over a period of time.
To test this theory, researchers led by Karen Lu at the University of Texas MD Anderson Cancer Center in Houston, did an 11-year study involving more than 4,000 post-menopausal women who received yearly CA-125 tests. In total, 10 women had surgery because their test results looked worrisome when analyzed with the algorithm. Of those, four were discovered to have early stage ovarian cancer, five had tumors considered benign, and one had endometrial (lining of the uterus) cancer.
Writing in the journal Cancer, the researchers said a lot more work must done before this screening approach is ready for the general public.
I asked Dr. Allan Covens, head of gynecologic oncology at Sunnybrook Health Sciences Centre, what he thought of the U.S. study. He believes it’s promising because only a small number of women were referred to surgery. In other words, there were not many false alarms.
But a better measure of this screening approach will come from a much bigger study, involving 200,000 women, now taking place in Britain, added Dr. Covens, who is also a professor of obstetrics and gynecology at the University of Toronto. The findings will likely be released in 2015.
Even if the British results are encouraging, the CA-125 test has some well-known limitations. Not all ovarian tumors produce detectable levels of CA-125, said Dr. Covens. The test could miss up to 20 per cent of ovarian cancers, according to some estimates.
It should also be kept in mind that ovarian cancer is relatively uncommon. About 2,600 women in Canada are diagnosed with ovarian cancer each year and 1,700 die from the disease, according to the Canadian Cancer Society. By contrast, an estimated 23,800 women in Canada will be diagnosed with breast cancer this year, and 5,000 will die from the disease.
So there would need to be some thought put into how a screening test should be used. Is it practical to screen the entire female population? Or, is it possible to just screen high-risk individuals like those with a family history of the disease?
Meanwhile, as the search for a reliable test continues, Dr. Covens noted that progress has been made in extending the lives of those diagnosed with advanced disease.
“People are living a lot longer than they used to,” said Dr. Covens. “For those people who we can [surgically] remove all their visible tumor, the median survival is eight or nine years now, which is dramatically different from 10 or 15 years ago when the median survival for most patients was in the three to five year range.”
