Pulmonary embolism (PE) is a serious condition that occurs when blood clots block the arteries that carry blood to the lungs. The symptoms depend on how big the blockage is and how much of the lung is affected. Some common signs are difficulty breathing, pain in the chest, cough, and blood in the mucus. Some other symptoms are fever, pain or swelling in the legs, fast or irregular heartbeat, sweating, skin that feels cold or looks blue, dizziness, and feeling faint.

Usually, a pulmonary embolism happens when a blood clot travels from the heart to the lungs, through the pulmonary artery. This is the artery that brings blood to the lungs. A clot can be so small that it does not cause any problems, but a big one can be very dangerous: it can get stuck in the artery and block a vessel completely.

To diagnose pulmonary emboli, a doctor may do a test that measures how well air and blood flow through the lungs, a CT scan that shows detailed images of the lungs, or a test that uses dye to see the blood vessels in the lungs.

Blood thinners can treat small clots and mild symptoms. Clot-dissolving medication may be needed for large, severe clots.

Risk in Cancer Patients

Cancer patients have a higher risk of PE than other people. They are about four times more likely to get venous thromboembolism (VTE), pulmonary embolism, and deep vein thrombosis (DVT) than the general population.

Venous thromboembolism (VTE) is a condition where blood clots form in the veins. PEs are one possible complication of VTE. Another one is deep vein thrombosis (DVT), when blood clots form in the deep veins, usually in the legs.

In patients with DVT, part of a clot may break off and travel to the heart and lungs. This can cause PE. But some patients may have PE without having DVT. What causes blood clots to form in the deep veins?

Some possible causes are:

  • Injury to a vein;
  • Damage to the inner lining of a vein;
  • Inflammation;
  • Surgery;
  • Serious injuries;
  • Some immune responses;
  • Inherited conditions (e.g. factor V Leiden);
  • Conditions that make the blood thicker;
  • Birth control pills;
  • Hormone therapy;
  • Staying in bed for a long time and long flights.

Clot-preventing medication is recommended for cancer outpatients who have a high risk of VTE, patients with myeloma, and patients who take immunomodulators. Patients usually get low-molecular-weight heparin (LMWH) as treatment. There are also oral blood thinners, but there is not much evidence that they work well.

A recent study showed that most cancer patients chose oral treatment instead of LMWH, which needs injection. But experts say that the treatment, along with other health problems, should be carefully thought about before changing to the oral agent.

Risk in Patients with Blood Cancers

According to early studies, blood cancers (e.g. leukemia, lymphoma, and myeloma) were generally less likely to increase the risk of blood clots than solid tumors (e.g. breast cancer and lung cancer).

However more recent studies counter this theory: the specific type of blood cancer and individual patient characteristics may be playing the key roles in increasing this risk.

Elderly Patients with Chronic Myeloid Leukemia (CML)

According to a 2016 study, elderly patients with Chronic Myeloid Leukemia (CML) present greater percentages of PE than patients without cancer.

It is worth noticing that the percentage of clotting problems did not increase in the patients taking tyrosine kinase inhibitors.

This suggests that underlying factors associated with cancer, rather than the treatment, drove the risk in these CML patients.

Acute Lymphoblastic Leukemia and VTE in Children

While acute lymphoblastic Leukemia (ALL) is a curable malignancy, especially in children, it is also associated with higher risks of VTE.

Pulmonary emboli are not common in children. However, leukemia and other malignancies can heighten the risk of childhood VTE and PE.

The main risk factors for VTE and PE include:

  • A central venous catheter;
  • Malignancies;
  • Chemotherapy.

2.1–16% of children with cancer contract VTE, while 2.6 to 36.7% of patients report catheter-related VTE.

According to a meta-analysis of children affected by leukemia, VTE was reported in 5.2% of children with Acute Lymphocytic Leukemia (ALL), the most common pediatric malignancy. However, reported rates ranged from 1 to 36%.

Acute Promyelocytic Leukemia

Blood clots are less common than bleeding in patients with acute promyelocytic leukemia, a rare type of AML.

This type of blood cancer affects the body’s coagulation system, which often leads to bleeding. Nosebleeds that won’t stop, or a cut that won’t stop oozing are common in these patients.

However, blood clots may still occur. Acute promyelocytic leukemia patients may experience calf swelling due to DVT, or chest pain and shortness of breath caused by PE.

Clotting Risk in Leukemia and Lymphoma

All types of cancer can increase the risk of VTE, according to a 2015 study. Depending on cancer categories, the extent of the risk may vary.

This study saw the lowest risk of VTE was with head and neck cancers, and the highest risk with brain cancer. Leukemia patients presented intermediate risk.

A particular increase in VTE risk is associated with the following cancer types:

  • Lymphoma;
  • Brain cancer;
  • Pancreatic cancer;
  • Digestive cancers (e.g. esophagus, gallbladder, bile system, small intestine).

Finally, while cancer patients may be at greater risk of pulmonary embolism, the overall chances of developing a pulmonary embolism are still relatively low. The use of central venous catheters can be life-saving for cancer patients, though it may increase the risk of VTE and PE.

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