Cancer and Blood Clots: A Complicated Connection

Blood clots are a complex condition that can be triggered by various factors, from prolonged inactivity to genetic predisposition. However, one often-overlooked cause is cancer.

Studies show that 4-20% of cancer patients experience blood clots, making them the second leading cause of death in these patients. But why does cancer increase the risk of blood clots?

Why Does Cancer Cause Blood Clots?

The reasons vary from patient to patient, but some key factors contribute to clot formation.

Dr. Jean Connors, a hematologist at Brigham and Women’s Hospital and the Dana-Farber Cancer Institute, explains:

"Several different factors increase the risk of blood clots in patients with cancer."

1. Certain Cancers Produce Clotting Substances

Some mucin-producing adenocarcinomas—cancers that originate in epithelial cells—release substances that trigger clot formation.

2. Tumors Can Physically Block Blood Flow

Larger tumors can compress blood vessels, slowing circulation and creating the perfect conditions for clots to form.

3. Cancer Treatments Can Increase Clotting Risk

• Chemotherapy can cause inflammation and damage blood vessels, increasing clot risk.

• Radiation therapy can also lead to blood vessel damage, making clot formation more likely.

Additional Risk Factors for Blood Clots in Cancer Patients

Aside from cancer, other risk factors can further elevate the risk of developing a blood clot, including:

• Family history of blood clots

• Hormone therapy (e.g., birth control, menopause treatments)

• Recent surgery, especially hip or knee replacement

• Pregnancy

• Sedentary lifestyle

• Smoking

• Obesity

By adopting a heart-healthy lifestyle, cancer patients may reduce their risk of developing blood clots.

Blood Clots as a Symptom of Cancer

For some patients, a blood clot may be the first sign of an undiagnosed cancer.

That was the case for Mark, a 49-year-old business owner, who was diagnosed with a submassive pulmonary embolism (PE). After further testing, doctors discovered that multiple myeloma (a type of cancer) had caused his clot.

"I was a ticking time bomb without anyone knowing," Mark said. "I feel extremely fortunate to have received treatment in time."

Studies indicate that up to 10% of patients diagnosed with a blood clot are later found to have cancer within a year.

However, routine cancer screening for every patient with a blood clot is not always necessary.

A 2015 study published in the New England Journal of Medicine found that using CT scans to screen clot patients for cancer did not significantly improve cancer detection rates compared to standard tests like blood work and chest X-rays.

Dr. Connors emphasizes the importance of regular cancer screenings, such as:

• Mammograms

• Pap smears

• Colonoscopies

Treating Blood Clots in Cancer Patients

The American College of Cardiology (ACC) recommends low-molecular-weight heparin (LMWH) as the preferred treatment for blood clots in cancer patients over warfarin or direct oral anticoagulants (DOACs).

Similarly, the American Society of Clinical Oncology advises that all hospitalized cancer patients be considered for anticoagulants to prevent blood clots.

However, many patients struggle with daily injections of LMWH, leading doctors to explore DOACs as an alternative. A 2017 study published in the New England Journal of Medicine compared:

• Edoxaban (a DOAC)

• Dalteparin (a low-molecular-weight heparin)

The results showed that both treatments were equally effective at preventing recurrent blood clots, but edoxaban was linked to a higher risk of bleeding—especially in GI cancer patients.

Dr. Connors cautiously supports using DOACs in carefully selected cancer patients, saying:

"While the results of this study are encouraging, I am still cautious about using DOACs in every cancer patient with VTE until more data are available."

Final Thoughts

If you or a loved one has cancer and blood clots, it’s essential to talk to your doctor about the best treatment options. While cancer increases clot risk, personalized care based on your medical history and lifestyle can help reduce complications. Regular screenings, proper anticoagulation therapy, and lifestyle modifications can all play a role in improving patient outcomes. For more information, speak with your healthcare provider to determine the best treatment plan for your specific case.