Blood clots are a normal part of your body’s response to injury. When you cut yourself, cell fragments called platelets rush to the injury site to seal up the damage and stop the bleeding.

Other blood clots aren’t helpful. Unnecessary clots can clog up blood vessels in your brain or lungs. That can lead to a dangerous blockage in blood flow.

Blood clots can be a side effect of both lung cancer and the drugs you take to treat it. It’s important to know the warning signs of a clot and get medical attention right away if you think you have one.

Lung cancer can increase the risk for blood clots inside your deep veins. This is called venous thromboembolism (VTE). People with cancer are four to seven times more likely to develop a clot than people without cancer. Cancer is responsible for about 1 out of every 5 cases of VTE.

Deep vein thrombosis (DVT) is a type of VTE. DVT is a clot in one of the deep veins inside your legs, and it can be serious.

A DVT blood clot can break free and travel through your bloodstream to your lungs. This is called a pulmonary embolism (PE), and it can be deadly if it cuts off blood supply. Blood clots can also travel to your brain and cause a stroke.

Up to 25 percent of people with cancer will eventually develop a blood clot. These can be painful, are serious, and must be treated. Blood clots are the second leading cause of death in people with cancer, after cancer itself.

Cancer cells damage healthy tissues as they multiply and spread. When your body senses damage to its tissues, it sends out platelets and clotting factors to repair the damage. Part of this repair process involves forming clots to prevent excess bleeding.

Cancer thickens your blood and releases the sticky proteins that form clots. Tumors can also press on blood vessels as they grow and stop the flow of blood. Whenever blood doesn’t move, clots can form.

Certain people with lung cancer are more likely to develop blood clots, including those who have:

  • non-small cell lung cancer (NSCLC)
  • adenocarcinoma
  • stage 3 or 4 lung cancer
  • chemotherapy or surgery to treat their cancer

Other factors that can increase your risk for blood clots further are:

  • being over age 65
  • being pregnant
  • smoking
  • infections
  • having obesity or being overweight
  • having a family history of blood clots
  • undergoing blood transfusions for anemia

Some cancer treatments also increase your risk for blood clots. Chemotherapy damages blood vessel walls and triggers the release of substances that cause clots to form. Platinum-based chemotherapy drugs such as cisplatin and the targeted drug bevacizumab (Avastin) are known for causing clots.

Lung cancer surgery is another risk. When you’re on the operating table and off your feet, blood pools in your veins, and clots can form. The hospital where you have surgery should take special precautions to prevent you from developing blood clots afterward.

Blood clots don’t always cause symptoms. These symptoms may indicate a blockage:

  • swelling, warmth, or pain in the back of the calf and thigh of one leg
  • redness of the skin
  • pain in your chest when you breathe deeply
  • sudden shortness of breath
  • fast heart rate
  • coughing up blood, which is less common

Call 911 or go to an emergency room right away if you have symptoms like these.

A blood test, CT scan, or ultrasound can confirm whether you have a blood clot. If you do have a clot, your doctors can give you medication to dissolve it and prevent new clots from forming. These will help you heal while your body dissolves the clot.

A higher risk of blood clots is just that, a risk. There are steps you can take to prevent clots from forming.

You may need to take a blood thinner such as heparin or other medications to prevent blood clots. Your doctor will weigh your risk of blood clots against your risk of bleeding from blood thinners when deciding to prescribe these for you.

You may need blood thinners after lung cancer surgery, when your risk of blood clots is higher. You can also wear compression stockings or socks to keep the blood moving in your legs and prevent clots from forming while you recover.

Blood clots probably aren’t at the front of your mind when you have cancer. Your focus is on treating your disease and wiping out as much of your cancer as possible. Still, it’s good to know about them.

If your doctor doesn’t talk to you about blood clots, bring it up. Ask about your risk, and what you can do to avoid developing a clot. Be on the alert for symptoms like swelling and pain in your leg, and get medical help right away if you have them.