Blood clots are a complicated disease that can be caused by many different things, from sitting too long to an inherited genetic risk. One cause that many people are unfamiliar with is cancer.

Patients with cancer, diagnosed or undiagnosed, are at risk for developing blood clots, which occur in 4% to 20% of patients. It is the second leading cause of death for these patients. It’s important for patients, those with cancer and those only affected by blood clots, to understand the connection between the two.

Why does cancer cause blood clots?

The answer to “why?” is not a simple one and can vary from patient to patient.

“There are several different factors that increase the risk of blood clots in patients with cancer,” said Dr. Jean Connors, a hematologist that works with both Brigham and Women’s Hospital and the Dana-Farber Cancer Institute.

For some patients, the type of cancer they have can trigger blood clots.

“Some cancers actually produce substances that are pro-coagulant,” explained Dr. Connors. According to Dr. Connors, mucin producing adenocarcinomas, types of cancers that arise from epithelial cells, are especially pro-thrombotic (meaning they can promote the creation of blood clots). They release substances that activate the clotting cascade and produce clots in the areas where they are found.

Blood clots can also be triggered by tumors that cause the ‘Mass Effect.’

“These tumors compress the blood vessels and slow the blood flow, setting up the ideal state for a clot to form,” said Dr. Connors.

For other patients, different cancer treatments can make them prone to blood clots.

“Many chemotherapy drugs are pro-thrombotic, some more so than others,” Dr. Connors explained. “They can cause inflammation and vascular endothelial damage. They create a situation that is prime for clotting.”

Radiation therapy can also leave patients at risk for developing a clot. The radiation can damage the body’s vascular endothelium, making it inflamed and pro-thrombotic.

Additional risks for blood clots can compound the risk from cancer.

If a patient already has established risk factors for a blood clot, cancer only adds to that risk. Additional risk factors can include:

  • A family history of blood clots
  • Hormone therapies, such as birth control or menopausal treatments
  • Surgery, especially on the hip or knee
  • Pregnancy
  • A sedentary lifestyle
  • Smoking
  • Obesity

Several of these risk factors can be controlled through living a heart healthy lifestyle. Patients with cancer should try to adopt heart healthy habits to help them lower their risk of developing a blood clot.

Blood Clots as a Symptom of Cancer

For some patients, the blood clot comes before the cancer diagnosis. That was the case for Mark, a business-owner and family man, who was diagnosed with a submassive PE at 49 years old.

After receiving treatment at Massachusetts General Hospital, Mark’s doctors followed up with him to find out why he had experienced an unprovoked blood clot (unprovoked meaning there was no known cause).

His doctors discovered that his blood clot had been caused by multiple myeloma, a dangerous form of cancer.

Because of this discovery, Mark was able to get the treatments he needed.

“I was a ticking time bomb without anyone knowing,” said Mark. “I feel extremely fortunate.”

“I feel better every day. I get stronger every day,” he remarked, praising the nurses and doctors he’s been working with.

Up to 10% of patients with an unprovoked clot are diagnosed with cancer within a year of their blood clot. Despite the fact that blood clots can be a sign of undiagnosed cancer, screening for cancer is not immediately done for patients diagnosed with an unprovoked blood clot. Studies have shown that screening every patient may be ineffective and not beneficial.

A study, “Screening for Occult Cancer in Unprovoked Venous Thromboembolism,” published by the New England Journal of Medicine in 2015, investigated whether patients with unprovoked blood clots should get extra radiology scans to check for cancer. They found that the screening with abdominal and pelvic CT scans did not detect any more cancers than standard screening tests, such as routine blood work and chest x-rays. They also found that the screening didn’t detect significantly more occult cancers, shorten a patient’s time to cancer diagnosis, or reduce the number of cancer-related deaths among trial participants.

“Not everyone with a clot has cancer,” Dr. Connors stressed. The best way to prevent cancer is by ensuring patients receive their age appropriate cancer screenings, such as mammograms, regular pap smears, and colonoscopies.

However, Dr. Connors did highlight the importance of doctors reacting to their blood clot patients’ additional symptoms.

“You should check up on symptoms,” she said. For example, if a patient has persistent abdominal pain or unexplained bleeding and an unprovoked blood clot, a CT scan or other tests may be in order.

Treatments for Blood Clots in Cancer Patients

The American College of Cardiology (ACC) provides specific outlines for how doctors should treat blood clots. For patients with cancer, they recommend low molecular weight heparin over warfarin or any of the direct oral anticoagulants (DOACs).

The American Society of Clinical Oncology recommends that all hospitalized cancer patients be considered for an anticoagulant to prevent blood clots. As with the ACC, the American Society of Clinical Oncology also recommends low molecular weight heparin as the preferred treatment for the initial blood clot and continuing treatment of cancer patients with blood clots.

When treating patients, doctors must balance these guidelines with patient preference and patient history. Patients on low molecular weight heparin must deal with injecting themselves with the medication every day, which many patients have trouble with.

A very recent report on the use of one DOAC, edoxaban, compared to treatment with dalteparin, a low molecular weight heparin, for patients with cancer and blood clots was published in the New England Journal of Hematology in December 2017. This study found that patients treated with edoxaban had the same composite risk of developing both recurrent blood clots and major bleeding. It appears that edoxaban might have been better at preventing recurrent blood clots than dalteparin, but there was an increase in bleeding. This was primarily seen in patients with GI cancers.

“Even before publication of the results of this study, I would use the DOACs in very carefully selected cancer patients, such as people who have good renal function, who have minimal risk of bleeding, and for whom they’re likely going to be effective,” explained Dr. Connors, referring to the study that compared edoxaban and dalteparin.  “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.”

If you’re a patient dealing with blood clots or cancer, talk to your doctor about any concerns that you may have. Only your doctor is familiar with your individual case and can provide personalized care.

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