What Is a Pulmonary Embolism, Catherine O’Hara’s Cause of Death?

Catherine O’Hara died of a pulmonary embolism and had rectal cancer at the time of her death, NBC News confirmed on Feb. 9.

A pulmonary embolism, or a blood clot in the lungs, was the immediate cause, according to her death certificate, obtained by NBC News, with rectal cancer as the sequential cause of death.

The comedic actor who made generations of people laugh with her roles in “Home Alone,” “Best in Show” and “Schitt’s Creek,” died on Jan. 30. She was 71.

O’Hara died at her home in Los Angeles “following a brief illness,” Creative Artists Agency, which represented O’Hara, previously said in a statement to NBC News.

A Los Angeles County death certificate stated that she had been treated since March of last year and last saw her oncologist in late January. It also showed that she was cremated.

What Is a Pulmonary Embolism?

O’Hara’s “immediate cause of death” is listed as a pulmonary embolism, which is a sudden blockage in a lung artery. It usually happens when a blood clot deep in the leg or pelvis breaks loose and travels to the lungs, according to the National Library of Medicine. As a result, blood flow to the lungs becomes restricted, lowering oxygen levels and increasing blood pressure.

Pulmonary embolisms require fast treatment to prevent death or permanent illness. About 33% of people with pulmonary embolisms die before they are able to get treatment, according to the Cleveland Clinic. They are the third most common blood vessel condition, after heart attack and stroke.

People with pulmonary embolisms will have only mild symptoms for days to weeks, while others may get more severe symptoms within minutes of developing one.

Having cancer, as O’Hara did, can increase the risk of developing a pulmonary embolism. That’s because when the cancer spreads in the body, more clots develop, and certain cancer treatments can increase the risk of blood clots, according to MD Anderson. Being older, undergoing surgery and struggling with mobility can also increase the risk of pulmonary embolism.

Between 3-10% of cancer deaths are due to pulmonary embolism, MD Anderson estimates.

Pulmonary Embolism Symptoms

Pulmonary embolism usually first manifests as sudden shortness of breath and unexplained chest pain that worsens with heavy breathing, according to Cleveland Clinic. However, not all people experience symptoms.

Other signs include:

• Fast breathing
• Wheezing
• Sharp pain in the arm, back, neck, shoulder or jaw
• Cough, possibly with bloody mucus
• Pale or clammy skin
• Rapid heart rate
• Excessive sweating

• Anxiety, lightheadedness and fainting

What Is Rectal Cancer?

Rectal cancer is listed as an underlying cause of O’Hara’s death.

This cancer starts in the rectum, the last 6 inches of the digestive system where stool is stored until it passes through the anus, according to the American Cancer Society.

It accounts for about 30% of new colorectal cancer cases in the U.S.

Rectal bleeding is the “red flag symptom” to be concerned about, Dr. Daniel Chung, a gastroenterologist at Massachusetts General Hospital, previously told TODAY.com.

Other symptoms include a change in bowel habits such as sudden constipation, abdominal pain and unexplained weight loss.

O’Hara’s Health History

In a 2020 interview, the actor said she had situs inversus, a condition where the heart is located on the right side of the body, not the left. She said that her organs were “flipped.”

The National Institutes of Health describes it as “a mirror image of normal anatomy.”

The condition is caused by genetic mutations, with congenital heart defects present in 5-10% of affected people, it notes.

O’Hara said she found out about her unusual anatomy as an adult when a doctor ordered an EKG as part of routine medical tests.

That’s a common experience. The reversed organs are still usually functional so people may not have any symptoms or complications, according to the Cleveland Clinic.

O’Hara’s Legacy

O’Hara was born in Canada and grew up as the sixth of seven children in Toronto, Ontario. Her parents were funny, and a sense of humor was “demanded more than encouraged” in her home, she told TODAY’s Willie Geist in 2024.

“When you have that many people at the table, you better have something funny to say,” she noted.

O’Hara became famous for playing movie and TV moms, including the over-the-top matriarch in “Schitt’s Creek,” the eccentric stepmom in “Beetlejuice,” and most famously the mom who accidentally leaves for a trip without her son Kevin in the 1990 hit comedy “Home Alone” and the sequel.