How Can Rectal Cancer Cause a Pulmonary Embolism?

Following the news that actress Catherine O’Hara died of a pulmonary embolism with rectal cancer noted as the underlying cause, many people are asking: How does cancer in the rectum lead to a fatal blood clot in the lungs?

People with cancer have a higher risk of developing blood clots. Surgery and cancer treatments can also increase the risk.  

How does cancer increase the risk of blood clots?

Cancer cells actively release substances that trigger the body's clotting system. In a healthy person, blood clots only when necessary (like when you cut your finger) to stop bleeding. In a person with cancer, the tumor cells trick the body into thinking it needs to clot even when there is no injury.

There are other ways that cancer can increase the risk of developing blood clots. For example, tumors in the pelvis, like rectal cancer, can physically press against large veins, slowing down blood flow in the legs. When blood moves too slowly, it tends to clump together. This creates an environment where clots can form easily, usually in the deep veins of the legs. This condition is known as deep vein thrombosis (DVT).

All or part of a DVT can break off and travel through the body, including to the lungs, leading to a pulmonary embolism.

What is a pulmonary embolism?

A pulmonary embolism (PE) occurs when a blood clot breaks loose from its original location and travels through the bloodstream to the lungs. Once there, it gets stuck in an artery, blocking blood flow.

This blockage prevents leads to decreased oxygen availability for the rest of the body. It also puts strain on the heart, which must pump harder against the blockage. If the clot is large enough, or if there are multiple clots, it causes heart failure or sudden death.

For cancer patients, a pulmonary embolism is a leading cause of death, second only to the cancer itself. Pulmonary embolisms often happen suddenly. However, in many cases, the clot starts in the leg as a DVT. Identifying and treating the clot in the leg typically prevents it from traveling to the lungs.

What causes rectal cancer?

Risk factors for rectal cancer include:

• Age: The risk increases as you get older, though rectal cancer rates are rising in people under 50.
• Family history: Lynch syndrome and other inherited gene mutations significantly raise your risk.  Even without an inherited mutation, having a family history of colorectal cancer can increase your risk of developing it.
• History of inflammatory bowel disease: Chronic inflammation from ulcerative colitis or Crohn's disease damages cells over time.
• Lifestyle factors: A diet low in fiber and high in fat or processed meats, a sedentary lifestyle, diabetes, obesity, smoking, and heavy alcohol use all contribute to higher risk.

Signs of rectal cancer

Cancer screenings increase the chances of finding certain cancers early, when they might be easier to treat. Additionally, a colonoscopy can actually remove potentially pre-cancerous growths before they ever develop into cancer. You should schedule an appointment for a rectal cancer screening if you notice:

• A change in bowel habits. This includes diarrhea, constipation, or more frequent bowel movements that last for more than a few days.
• Blood in your stool. This usually appears bright red, though it can sometimes look very dark.
• Stool consistency changes. Stools that appear very narrow or ribbon-like could indicate a blockage.
• Abdominal pain. This could include persistent cramping or gas pain.
• Weakness and fatigue. This is often caused by anemia from slow blood loss.
• Unintended weight loss.

Rectal cancer screening options include colonoscopy, a fecal immunochemical test (FIT Test), stool DNA test (such as Cologuard), or a specific type of CT scan called a CT colonography.

Is rectal cancer the same as colon cancer?

Colon and rectal are referred to collectively as colorectal cancer. While the two types of cancers share some symptoms, they are different.

Colon cancer affects the colon, which makes up the first five feet of the large intestine. Rectal cancer affects the rectum, the final six inches that connects the colon to the anus. Because the rectum sits in a tight space within the pelvis, crowded by other organs and blood vessels, cancer here requires different treatment approaches compared to colon cancer.

Both cancers have similar risks when it comes to the risk of blood clots. Whether the tumor starts in the colon or the rectum, the presence of cancer cells changes how your blood functions, significantly increasing the risk of clotting.

How can you prevent blood clots from cancer?

Warning signs of cancer-associated blood clots are sometimes overlooked. 

Symptoms that can be associated with a pulmonary embolism include shortness of breath, chest pain or dizziness and lightheadedness. Signs or symptoms of a DVT in the leg may include asymmetrical swelling of one leg compared with the other, sometimes associated with pain or redness of the skin. A person with cancer may already be experiencing some of these symptoms due to the disease or chemotherapy. This makes it easy to miss the warning signs of a DVT or pulmonary embolism until it is an emergency.

Doctors may prescribe blood thinners, known as anticoagulants, as a prevention method. Cancer patients also are encouraged to move around frequently to prevent blood from pooling in their legs.

Blood clots are an important part of understanding how cancer impacts the entire body. Screening tests can help identify cancer early, when it’s most treatable. If you have a family history of colorectal cancer or notice any symptoms, do not wait – schedule a screening today.

Learn more about colon, rectal and anal cancer care at Ochsner.