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• Posted October 22, 2025

How Does Cancer Kill People? New Theory Suggests Blood Clots

What kills cancer patients is where their malignancy spreads in their body, rather than the cancer itself, a new study says.

If tumors spread into major blood vessels, they can spark blood clotting that contributes to organ failure, researchers recently reported in the journal Nature Medicine.

That’s why some people with advanced cancer die quickly, while others survive even though cancer has spread throughout their bodies, researchers said.

“The big question we were trying to answer: What kills cancer patients? Why do they die one specific day rather than six months earlier or later?” senior researcher Dr. Matteo Ligorio said in a news release. He’s an assistant professor of surgery at UT Southwestern Medical Center in Dallas.

Cancer kills about 600,000 Americans each year, but what actually ends their lives has been a mystery, Ligorio said.

To investigate, researchers analyzed the cases of more than 100 patients who died from colon, lung, ovarian, liver or pancreatic cancer. They also recruited 31 terminally ill patients in hospice, including 21 with solid tumors and 10 with other conditions.

When the patients died, at an average of 38 days after entering the study, Ligorio performed an autopsy to examine their major blood vessels.

Unlike patients who died from other causes, those with cancer typically had tumors that had grown into their blood vessels. CT scans showed these malignancies were present in the weeks or months preceding death.

Blood samples also revealed a sharp increase in the number of cancer cells in the bloodstream just before death.

Ligorio strung these findings together to create a new theory regarding the reason cancer patients ultimately die.

When tumors enter major blood vessels, microscopic cancer particles might break off into the bloodstream, making blood more likely to clot.

Those clots would cut blood flow to the patient’s organs, leading to organ systems failure that ultimately causes death.

To validate the theory, researchers then examined CT scans from 1,250 German cancer patients. The found most of the patients had tumors infiltrating their major blood vessels.

The team is now setting up a clinical trial to see whether treatments to limit the spread of cancer into blood vessels could extend a cancer patient’s survival.

“Surgery or radiation to treat tumors approaching large blood vessels could potentially transform how we diagnose, manage and treat patients with cancers,” lead researcher Dr. Kelley Newcomer, an associate professor of internal medicine at UT Southwestern, said in a news release.

More information

Cancer Research UK has more on how cancer kills you.

SOURCE: UT Southwestern Medical Center, news release, Oct. 16, 2025