the problem with ovarian cancer screening: 'overlooked and underfunded'
6 minute read
advancements like multi-cancer early detection (mced) blood tests can catch some cancers early in the bloodstream—but ovarian cancer remains a difficult exception.
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there is no standard way to screen for ovarian cancer. because of that, this type of cancer is often diagnosed later on in the progression of the disease, leading to worsened outcomes.
many other cancers have screening, so why not ovarian? well, it has a lot to do with how it develops.
“the name itself is a misnomer,” said dr. annie leung, gynecologic oncologist. “the cancer cells don’t actually start from the ovary itself. it’s actually the fallopian tube that is next to the ovary that is the cause in the majority of ovarian cancer.”
only about 25 to 30 per cent of ovarian cancers actually originate in the ovary.
the origin of ovarian cancer
it’s not just where it starts that has caused some difficulties in creating a screening test. it’s also about how the cancer itself presents. it typically doesn’t form a large tumour or mass, unlike many other cancers.
“you can picture the fallopian tubes. it has very soft, gentle, it has finger-like processes, and it’s near the ovary, but when this cancer starts there, it flakes off like aerosol or dandelion fluff, and it goes into the abdomen. it has access to the whole of the abdomen,” said dr. lucy gilbert, chief of gynecological cancer services for mcgill university health centre. “it goes and lodges behind the liver just one, two, three cells at a time.”
the reason the cells have such free access to the rest of the abdomen is that the fallopian tubes are connected only to the uterus. they are otherwise free-floating in the belly, so the cells, once they flake off, have free rein to roam anywhere. during that time, they may go to the ovaries, which “are the closest neighbour,” but “because they’re so small, by the time we are able to detect it by ultrasound, ct scan, or blood test, they’ve already gone to other places,” said dr. leung.
in some cases, because endometrial cancer also spreads throughout the abdomen, it can sometimes be used interchangeably with ovarian cancer, which results in further difficulty with diagnosis and treatment.
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“if you don’t call it by its name, if you don’t nail it, if you’re not precise, then you won’t advance in your treatment,” said dr. gilbert.
there are also very few symptoms during this time because, as the disease develops and spreads, there’s nothing large enough for the body to form a response.
“we like cancers that make a lump, because if you make a lump, it causes symptoms,” said dr. gilbert. “[but] if it’s like fine, microscopic dust, what can you use? why are microplastics so dangerous? whenever something cannot be seen, and it goes all over, you have a problem with it.”
the type that does start in the ovary will form a mass, which may make it easier to detect. however, as many as 80 per cent of all ovarian cancers are diagnosed in either stages three or four.
“at that point, it’s particularly challenging to treat. women often go into recurrence,” said tani vrionis, chief executive officer of ovarian cancer canada.
why current screening tests fail to detect ovarian cancer
there are many screening test options for cancer, including a blood test called the multi-cancer early detection test (mced). these can detect cancers in the body that enter the bloodstream early enough in the process that finding out that way can help to stop it from progressing, leading to better outcomes.
however, for ovarian cancer, these tests may not be viable.
“if you look at colorectal cancer and breast cancer, they are in organs that have a rich blood supply, and the cancer cells enter the bloodstream and the lymphatics, and on the one hand, it’s very bad, but on the other hand, you can detect it,” said dr. gilbert.
but in ovarian cancer, the peritoneal cavity is covered with a “beautiful, fine peritoneum” like saran wrap that coats the organ to create a vacuum-like space. why is that an issue? because that seal doesn’t allow the cancer to make it into the bloodstream as quickly, rendering the mced test less viable.
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ultrasounds are also out because the tiny cellular development of cancer in the fallopian tubes and ovaries just isn’t big enough to be detected.
“ultrasound is usually only able to detect a mass when it’s already more than five millimetres or one centimetre,” said dr. leung. “at that point [when it gets that big], it has had a chance to spread.”
another testing option, the cancer antigen 125 (ca125) test, which looks for an increase in the specific ca125 protein to detect cancer is also not an option. the protein itself can seep into the blood after being irritated, and while ovarian cancer does irritate the lining of the abdomen, it doesn’t always rise in people with ovarian cancer.
“you need quite a big volume of ovarian tumour in order to cause that irritation and for the protein level to go really high to a point where we detect it,” said dr. leung. “the second limitation is, you can imagine, other things that can irritate the lining and can make the ca125 go up.”
things such as inflammatory bowel disease, endometriosis, or even a menstrual cycle can all irritate the lining to the point that the c125 goes up. for all of these reasons combined, the end result is that this particular test is also unreliable at early detection of ovarian cancer.
a research study dr. gilbert was involved in further debunked c125 and its ability to detect ovarian cancer early enough, noting that in the results, “c125 is too late.”
the future of ovarian cancer screening
there are many ongoing research projects geared toward finding something that can detect ovarian cancer earlier, but because this type of research has been “overlooked and underfunded” for decades, notes vrionis, the industry is playing catch-up with other cancers that have received much more attention.
“we haven’t been able to move the needle on much of the really important pieces, and one of those is a screening test,” said vrionis. “we’ve seen remarkable advancements in other cancers, from prostate cancer to breast cancer to colorectal cancer, because of that screening. we are making up ground now in ovarian cancer research.”
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the last decade is what has truly turned things around for ovarian cancer, but there are still some ways to go before a screening test is possible. that said, researchers such as dr. gilbert are working tirelessly to identify potential options.
one potential option is a genomic tap test, which looks for cancer fragments in the form of gene mutations. the test, called doveegene, works similarly to a pap test and can detect both ovarian and endometrial cancer by looking for abnormal cells and dna changes that indicate they are cancerous.
“we applied it prospectively in a trial of 5,000 people, so we have been at this for ages,” said dr. gilbert. “it’s not easy, but we’re not looking for an easy solution, and we’re not looking for gimmicks because i do at least two end-of-life discussions every week. so, for me, it’s not about papers; it’s not about publications; it’s not about a gimmick. what can we find so that we do right by women?”
the test itself is more invasive than a standard blood test, but it’s better than no alternative at all.
“until somebody comes up with something better, we’re prepared to do it,” said dr. gilbert.
while the results of the study itself are not yet available, dr. gilbert notes it has been highly effective, and when the future looks brighter in terms of screening for ovarian cancer, everybody benefits.
“this is one of the most important women’s health issues,” said vrionis. “of the 3,100 women diagnosed this year, only 44 per cent are expected to live for the next five years. so, these are mothers, grandmothers, aunts, sisters, cousins, friends, all experiencing this disease, and we need to change that trajectory and change those outcomes.”
she continued, “it’s just really important in that women’s health space, which has so much attention right now, that we talk about this particular incidence. this can be changed, and it can be changed with more investments and more awareness.”
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