Knee Pain May Be the First Sign of Lung Cancer - Verywell Health

While knee pain is usually related to injury or joint disease, it can be a sign of lung cancer in very rare instances.

If you know that you have a high risk of lung cancer because of smoking, genetics, or environmental exposure, you should get medical attention for any new symptoms, including joint pain. You may want to discuss the pros and cons of a cancer screening with your healthcare provider even if you don't have any of the "typical" signs of lung cancer.

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How Lung Cancer Can Cause Knee Pain

Knee pain may occur if a tumor spreads to connective tissue areas, or it may be the result of unusual complications associated with lung cancer.

Metastases

While lung cancer is most commonly associated with metastases to the brain, lymph nodes, liver, and adrenal glands, it can spread almost anywhere, including the synovial tissue. This is a type of connective tissue in the protective membranes surrounding the body's joints.

When lung cancer metastasizes to these areas of the body, it is usually a lung adenocarcinoma. The joints most likely to be affected are the knees.

When the knee is impacted in this way, symptoms may include:

• Pain
• Swelling
• Decreased ability to stand
• Impaired ability to straighten the knee

Surgery to remove the entire tumor is usually the first course of treatment for cancer in the synovial tissue. Chemotherapy may also be recommended to increase the chances of eliminating all of the malignant cancer cells. 

Paraneoplastic Syndromes

People with lung, ovarian, lymphatic, or breast cancer are at risk of developing paraneoplastic syndrome, a rare complication in which cancerous tumors cause organ or tissue damage that can trigger the production or release of hormones or other chemicals. Paraneoplastic syndromes affect approximately 10% of all people with lung cancer.

Paraneoplastic syndromes are thought to happen when cancer-fighting antibodies or white blood cells (known as T cells) mistakenly attack normal cells, especially in the nervous system or the endocrine (hormone) system.

Rheumatic and neurologic tissue are among the most commonly affected by paraneoplastic syndromes related to lung cancer.

Hypertrophic Pulmonary Osteoarthropathy (HPOA)

This rare type of paraneoplastic syndrome can be the first sign of lung cancer. Substances secreted by a lung tumor or made by the body in response to a lung tumor can cause swelling and inflammation.

Signs of HPOA may include:

• Painful inflammation and swelling in the knees, as well as the ankles, wrists, and elbows
• Clubbing (swelling of the ends of the finger)
• Koilonychia (spoon-shaped nails)

Once the tumor is removed, the knee pain or other symptoms related to HOA should improve. Treatment may also include nonsteroidal anti-inflammatory drugs (NSAIDs) or bisphosphonates, medications typically prescribed to treat osteoporosis.

Knee Pain as a Symptom of Lung Cancer

Both monoarthritis (pain in one joint) and polyarthritis (pain in multiple joints) have been identified as possible signs of lung cancer. Sometimes, these symptoms can be misdiagnosed.

The connection between knee pain and lung cancer can easily be missed because the rate of arthritis problems occurring with lung cancer is very low. 

• Arthritis symptoms due to a paraneoplastic syndrome occur in approximately 0.24% of lung cancer patients. 
• HPOA incidents among lung cancer patients range from 0.72% to 17%.
• Researches have only reported 48 cases of synovial metastasis, and only a fraction of those incidents are related to knee pain.

If you have lung cancer, your knee pain is more likely to be related to other causes and is rarely a symptom of your lung cancer.

If you have rheumatoid arthritis (RA), your knee pain is likely related to your arthritis. However, you should discuss your risk of lung cancer with your healthcare provider. Those with RA are eight times more likely to develop interstitial lung disease, which puts you at risk for lung cancer.

Diagnosis

If you have lung cancer and knee pain, your healthcare provider will first look for the obvious causes of joint disease or injury.

The connection between knee pain and lung cancer may only be found if your pain persists or if your discomfort spreads to other joints.

If you haven't been diagnosed with lung cancer, you might get tested for any of the following reasons:

• Signs of a paraneoplastic syndrome, such as clubbing
• X-rays of your knee are concerning
• Your joint pain doesn't respond to treatment

Computed tomography (CT) scan of the chest and a biopsy of the lung may be ordered to confirm a cancer diagnosis.

Treatment Options

If lung cancer is identified as the cause of your knee pain, your treatment will focus on removing or reducing the size of your tumor via surgery, chemotherapy, and/or radiation.

The type of surgery and the course of chemotherapy and radiation will depend on where the tumor is located, its size, and its type.

Your healthcare provider may also prescribe steroids, high-dose intravenous immunoglobulin, or irradiation.

A Word From Verywell

Lung cancer incidence and treatment has changed over the years. Today, young, non-smoking women are more likely to develop the disease in the form of lung adenocarcinoma. These cancers grow in the outer regions of the lungs undetected for a long time. You may not have classic symptoms of lung cancer until these tumors enlarge, or you may have vague symptoms that are easily ignored such as shortness of breath, unintended weight loss, or a vague sense of being unwell.

If knee pain or other unusual health symptoms arise, they might be a sign of lung cancer. Discuss any new problems with your healthcare provider; it's better to get checked out and determine the root cause than let it go and possibly face an advanced-stage disease down the road.