Now, researchers from Oxford University have discovered a special protein in the fallopian tubes of people with ovarian cancer, which could be used to help doctors detect the disease in its earliest stages.
They also identified an enzyme that makes ovarian cancer more deadly.
Their results, published in two journals, provide new research routes for scientists trying to detect and beat the disease.
Ovarian cancer is the fifth most common cancer for women in the UK, with about 7,100 new cases each year.
The symptoms can be difficult to recognise, particularly in its early stages, as they are often the same as symptoms of other less serious conditions, such as irritable bowel syndrome (IBS) or pre-menstrual syndrome (PMS).
If detected early enough, ovarian cancer can respond well to chemotherapy. However if it goes undetected and spreads, it becomes resistant to treatment and far more likely to prove fatal.
In their first paper, published in the online journal EBioMedicine, researchers showed that levels of a protein called SOX2 are much higher in the fallopian tubes of people with ovarian cancer.
It is also prevalent in some people who are at high risk of developing ovarian cancer, such as those with inherited mutations in BRCA1 and BRCA2 genes.
“Ovarian cancer can be undetectable for up to four years and only a third of people with the cancer get an early diagnosis,” said Professor Ahmed Ahmed, from the MRC Weatherall Institute of Molecular Medicine at Oxford University.
“A test for SOX2 could not only help detect cancers early but in some cases would enable us to detect a tumour before it becomes cancerous.
“Early treatment hugely improves the odds for patients, so early detection is essential. However, there is still a lot of work to be done because detecting SOX2 in the fallopian tubes is not an easy task.”
In their second paper, published in the journal Cancer Cell, the team identified an enzyme that enables ovarian cancer to spread.
When ovarian cancer spreads, it usually does so to the omentum, an apron of fatty tissue covering the small intestine. This can cause death by malnutrition, as the growing cancer obstructs the intestines.
“The omentum is rich in adipocytes - fat cells - and previous research found that the free fatty acids produced by these cells increase the spread of cancer,” Professor Ahmed explained.
“However, we have found that ovarian cancer could only proliferate - grow - in the presence of an enzyme called SIK2, which has a role in ‘burning’ fat to produce energy that is needed by the cancer cells to survive in the omentum.
“We continued this study of SIK2 and found that levels of the enzyme were higher in secondary tumours in the omentum than in the related primary tumours in the ovaries.”
A series of experiments confirmed that SIK2 not only played a key role in growing ovarian tumours, but in the metastasis that spreads them to the omentum.
Further experiments revealed the processes, know to medical researchers as ‘pathways’, involving SIK2 that support the development and spread of ovarian cancer.
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Professor Ahmed continued: “SIK2 is an important target for future treatments because it provides cancer cells with energy and also drives their increase in number.
“Our experiments showed that suppressing SIK2 disrupted these pathways, which in the human body would reduce the possibility of cancer cells spreading and ‘coming back’.”
Lord Maurice Saatchi, who campaigns for better access to cancer treatment, said: “By explaining these very detailed processes, the Oxford team are providing maps for researchers working on ways to treat and defeat cancer.
“The more we understand, the closer we come to beating not just ovarian cancer, but all types of cancer.”
Katherine Taylor, chief executive at research charity Ovarian Cancer Action, one of the study’s funders, hailed the findings as “promising”.
“Early detection and effective treatment are vital,” she said. “And these discoveries will hopefully bring us closer to both.”