A discovery into the cause of one of the deadliest cancers has been uncovered, which could hold the key to new treatments, scientists said.
The American Cancer Society estimates that 21,000 women will be diagnosed with ovarian cancer this year, and about 12,450 will die. Approximately 243,000 women are currently living with the disease.
Ovarian cancer is among the deadliest gynecological cancers because symptoms are often subtle and dismissed, meaning the cancer isn’t caught until it has spread and is harder to treat in late stages.
The cancer also spreads quickly, and until now, scientists didn’t know why.
A new study led by researchers at Nagoya University in Japan found that ovarian cancer cells ‘recruit help’ from mesothelial cells, which normally line the abdomen. These mesothelial cells ‘lead the invasion,’ allowing ovarian cancer cells to travel throughout the body as the mesothelial cells travel.
Together, these ‘hybrid’ cells travel further and resist chemotherapy better than just the ovarian cancer cells alone.
Lead author Dr Kaname Uno, a gynecological researcher, said: ‘[Cancer cells] manipulate mesothelial cells to do the tissue invasion work. They undergo minimal genetic and molecular changes and just migrate through the openings that mesothelial cells create.’
The ACS estimates a woman’s lifetime risk of being diagnosed with ovarian cancer is about one in 91 women. The five-year survival rate is about 50 percent, meaning just half of women with the disease are alive five years after diagnosis.
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However, if the cancer spreads, survival declines to 32 percent.
Among women, ovarian cancer is the 15th most commonly diagnosed, but it is responsible for the sixth-most deaths, falling behind lung, breast, pancreas, colorectal and uterine – all of which see more yearly cases.
According to the National Cancer Institute, ovarian cancer accounted for one percent of cancer cases in 2025, but two percent of cancer deaths.
Statistics do show, however, that cases and deaths are on the decline. The ACS credits the increased use of oral birth control and decreased use of menopausal hormone, as well as advanced screening and better treatments.
For the study, published in the journal Science Advances, researchers analyzed fluid from the abdominal cavity of ovarian cancer patients and found something ‘unexpected.’
The cancer cells were not alone in the fluid. Instead they had fused with mesothelial cells and formed ‘hybrid spheres.’ About 60 percent of all cancer spheres contained mesothelial cells.
When ovarian cancer develops, cancer cells break away from the original tumor and enter the abdominal fluid and float. The fluid flows through the body as people breathe and move, which carries the cancer cells to different spots in the abdomen.
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Once the mesothelial and cancer cells fuse, the cancer cells release a protein called TGF-β1, which transforms mesothelial cells and causes them to develop spike-like structures that cut through tissue.
The way ovarian cancer spreads is different from that of other cancers, such as breast or lung. Those cells enter the blood vessels and travel through the blood to reach distant organs.
But ovarian cancer cells avoid the blood and blood vessels altogether.
While the scientists discovered the floating and fusion of both types of cells, they were unable to determine how the cells worked together to spread the cancer so quickly and what actually happened while they were floating.
Uno said he was inspired to conduct this type of research after a patient of his was diagnosed with ovarian cancer just three months after she received clear screening results.
When current medical tools failed to the detect the cancer early enough to save her life, uno was motivated to figure out why ovarian cancer spreads so quickly.
Based on the discovery, the researchers believe it opens new treatment possibilities.
While current chemotherapy targets cancer cells, it ignores the mesothelial cells.
However, future drugs could block the TGF-β1 protein or prevent the fusion of different types of cells.
The research also suggests that doctors could monitor these cell clusters in abdominal fluid to predict disease progression and treatment response.
