A new computer test is helping doctors work out how long women with advanced ovarian cancer may survive.
The test, developed by experts at the Institute of Cancer Research in London, highlighted a "staggering" difference between those patients who would live for five years or more and those who would die before then.
It examines the cell "ecosystem" around secondary tumours - those in other parts of the body once cancer has spread from the ovaries.
The test gives a score according to whether the tumour spread is in one dominant cell type (giving a low score) or a more diverse cell population containing immune or connective tissue cells (high score).
Scientists found that survival rates were far worse for those women with a high score than for those with a low score.
Just 9% of women with a high score survived five years from diagnosis, compared with 42% of those whose cancer spread was dominated by one cell type.
The test gives a stronger predictor of poor survival than any of the current tools in use.
Doctors say it will identify those women who have the most life-threatening disease and who urgently need the most aggressive treatment.
About 7,000 women are diagnosed with ovarian cancer each year in the UK and the disease kills about 4,000 women a year.
Symptoms can be vague and include feeling bloated or full, irregular periods or bleeding, tummy or back pain and passing urine more often than normal.
Pain during sex and constipation are other possible signs.
Dr Yinyin Yuan, from the Institute of Cancer Research, said: "We used to think of tumours as simply a collection of cancer cells but we now know that they are often complex ecosystems made up of different types of healthy cell, too.
"Our study has revealed that diverse cell populations at the sites of cancer spread are a clinically important feature of particularly aggressive ovarian cancers.
"We have developed a new test to assess the diversity of metastatic sites and use it to predict a woman's chances of surviving their disease.
"More work is needed to refine our test and move it into the clinic but, in future, it could be used to identify women with especially aggressive ovarian cancers so they can be treated with the best possible therapies available on the NHS or through clinical trials."
Research on the test, involving 61 women with 192 secondary tumours treated at the Sun Yat-sen University Cancer Centre in China, was published in the journal Oncotarget.
It was funded by the Institute of Cancer Research, the Wellcome Trust and the Biomedical Research Centre at the Royal Marsden.
Professor Paul Workman, chief executive of the Institute of Cancer Research, said: "Ovarian cancer is more likely to spread than many other cancers because there is no barrier between the ovaries and the peritoneal cavity - the fluid-filled space in our torso that houses the body's organs.
"It's therefore critical that we understand more about the likely progression of disease among cancers that have spread and get better at tailoring our treatment for individual women.
"Finding ways of treating highly aggressive ovarian cancers is a huge challenge. But by knowing that a woman has an especially lethal form of disease, we can look to explore aggressive combination treatments and give women choices about the kinds of care they want to receive."
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