Catherine O’Hara’s death at 71 sent shockwaves through Hollywood.
The comedic actor has been remembered by former co-star Seth Rogen as “hysterical, kind, intuitive, generous” and by her contemporary and friend Martin Short as “the greatest, most brilliant, kindest, sweetest angel that any of us worked with.”
On Monday, details from her death certificate were revealed by TMZ, which confirmed pulmonary embolism as the cause of death on Jan. 30.
It also showed she’d been receiving treatment for rectal cancer since March 2025, leaving fans and medical professionals to speculate about whether the two were connected.
While rectal cancer is technically a different diagnosis than colon cancer, the two share many similarities and are frequently lumped together as colorectal cancer. But treatments for each are different, according to the Mayo Clinic, as are the rates of diagnosis.
The American Cancer Society estimates that as of this year, colon cancer is about twice as common as rectal cancer, with roughly 108,000 new colon cancer cases versus just under 50,000 rectal cases.
Overall rates of both, especially among older adults, have declined in recent decades thanks in part to better screenings. But for adults 50 and younger, the numbers of diagnoses have actually been climbing, increasing by almost 3% each year from 2013 to 2022 and puzzling doctors and cancer researchers.
O’Hara’s rectal cancer was listed as the long-term cause of death on the certificate, and may have contributed to the pulmonary embolism that ended her life. Here’s what to know about the connection.
What is pulmonary embolism?
A pulmonary embolism occurs when a blood clot blocks a major artery in the lungs, according to the Society for Vascular Surgery.
Typically, the clot (also known as a thrombus) forms somewhere else in the body, often a leg or arm, before it breaks off and travels through the bloodstream to the lungs, where it can restrict oxygen intake and prevent the heart from pumping properly.
What is the connection between pulmonary embolism and rectal cancer?
Research published last year in the Journal of Clinical Oncology states that pulmonary embolism is the leading cause of death in cancer patients. Across all types of cancer, the risk of pulmonary embolism is seven times higher than those without cancer.
But lung and gastrointestinal cancers (which include rectal cancer) face an even higher risk of pulmonary embolism.
In the early 2000s, a review of over 1 million Medicare patients hospitalized with cancer found that GI cancers were among the top 10 with the highest rate of deep vein thrombosis or pulmonary embolism out of 18 cancers reported.
How life-threatening is pulmonary embolism, and how is it treated?
Without immediate emergency intervention, pulmonary embolisms are very dangerous.
That said, over 90% of patients who are treated for pulmonary embolisms survive, according to the MD Anderson Cancer Center, though a second pulmonary embolism is “more lethal than the first one.”
If administered in time, treatments like blood-thinners are very effective. Other treatments depending on severity might include surgery to remove the clot, or the administration of “clot-busters” through an IV to break it up.
Who is most at-risk?
The MD Anderson Cancer Center says several cancer treatments can actually lead to blood clots, including chemotherapy and hormone therapy. “Patients who are older, undergo surgery, are immobile, obese or who have central venous catheters are at an increased risk of developing these clots.”
Other risk factors include a history of blood clots or clotting disorders, heart disease, severe cases of COVID-19, extended periods of inactivity from bed rest or long trips in a car or airplane, some hormonal birth control pills, smoking and sometimes complications from pregnancy or obesity.
