A pulmonary embolism tied to colorectal cancer killed Catherine O’Hara. Here’s how common the event is among cancer patients

Beloved comedy actress and Schitts Creek star Catherine O’Hara died at 71 last month due to a pulmonary embolism linked to rectal cancer.

Having cancer is a risk factor for the life-threatening blood clot, which results in more than 36,000 deaths each year, according to the American Heart Association.

But, how many cancer patients actually develop the condition? The percentage may be smaller than you might think.

Just around three percent of non-hospitalized cancer patients being treated with chemo die after suffering a pulmonary embolism. Among hospitalized patients, that percentage rises by seven percent.

“The risk of clotting increases as the cancer grows and spreads in the body,” MD Anderson Cancer Center says.

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Several types of cancer are more likely to cause these kinds of clots, which block blood flow to the lungs. Colorectal cancer is one.

The others include acute leukemia, brain cancer, breast cancer, kidney cancer, lung cancer, melanoma, pancreatic cancer and gynecological cancers - conditions that affect millions across the U.S.

Although chemotherapy, immunotherapy, hospitalization, obesity, infections, medications, catheters and sicknesses can also contribute to pulmonary embolisms in cancer patients.

“A single pulmonary embolism cause is sometimes never found. Because so many different things cause a pulmonary embolism and most of them can’t be eliminated or easily fixed, it is important to try to prevent them,” the center said.

Rates of several cancers are rising in young people, potentially leading to even more deaths related to pulmonary embolisms - though deaths in young cancer patients are on the decline.

Colorectal cancer is the only form of cancer that saw deaths tick up from 1990 to 2023, according to the American Cancer Society, and it’s now the leading form of cancer deaths in people under the age of 50.

Doctors are still working to figure out why all of this is happening, although our ultraprocessed diet and environmental factors have been cited as contributing causes.

Studies looking into pulmonary embolism deaths in cancer patients have also noted concerning increases.

A 2025 study including more than 27 million patients showed there was an increase in related deaths in cancer patients from 2011 to 2020, despite decreases in overall cancer-related deaths.

“These findings highlight a concerning increase in PE-related mortality in patients with cancer, indicating a need for further research and preventive interventions to improve outcomes,” the authors said.

The clot can damage the lungs and strain the heart, making it hard to breathe, raising your heartbeat, leading to excessive sweating or a stabbing pain, turning the skin blue and even resulting in you passing out.

O’Hara had trouble breathing when she was rushed to the hospital in Los Angeles, California, on January 30.

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So, how concerned should cancer patients be about this risk?

Pulmonary embolisms are common in lung cancer patients, according to researchers in China.

But there are also several risk factors that make people more likely to experience one.

“Patients who are older, undergo surgery, are immobile, obese or who have central venous catheters are at an increased risk of developing these clots,” MD Anderson says.

O’Hara also suffered from a congenital heart defect called dextrocardia that left her at an even greater risk.

Still, 90 percent of patients who are treated for pulmonary embolisms survive, MD Anderson notes. However, the second event is “more lethal.”