If You Can't See This, Get Checked for Cancer


Lung cancer is the third most common type of cancer in the U.S., and the single most deadly, according to the CDC. Unfortunately, that's in part because its symptoms typically don't appear until the more advanced stages of the disease. For this reason, experts are urging the public to learn one particular early sign of lung cancer, which often goes unrecognized by patients. They say that there's a simple way to test whether it's time to talk to your doctor: If you can't see this one thing, it's definitely worth requesting a screening. Read on to find out which surprising symptom could point to a lung cancer diagnosis, and which other benign causes could be to blame.

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Nail clubbing is linked to lung cancer.
kris4to / Shutterstock

When it comes to lung cancer, most people know to look out for respiratory symptoms. However, there's another little known symptom that experts warn could signal a lung problem:  clubbed fingers. You may recognize this symptom by the appearance of bulbous fingertips, and in many cases, a patients' nails will curve downward. While it is not always linked to lung cancer, this is considered the most common cause for fingernail clubbing, according to experts from Mount Sinai.

If you do notice the symptom, your doctor will likely run a range of tests to determine the exact cause. "Any good doctor who sees someone has clubbing will know that they may have some sort of lung disease, heart disease, or gastrointestinal disease," Eric Presser, MD, a thoracic surgeon and member of First California Physician Partners, told Health in 2020.

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If you can't see a "diamond gap" when pressing your fingernails together, it could be a sign of cancer.

Experts say there's one way to test for finger clubbing at home. While it's no replacement for a visit to your doctor's office, it could be the first step in evaluating your likelihood of an underlying condition.

This self-exam is known as both the "Schamroth's window" test and the "diamond gap" test. To try it, press the fingernails on your two index fingers together like this. If you can't see a diamond shaped gap of light between your nails, it could be a sign that you've got finger clubbing or an underlying condition.

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Look out for these other signs of lung cancer.

According to the American Cancer Society (ACS), most people with lung cancer will not notice symptoms until the cancer has already spread. However, if you do notice early symptoms, it's important to talk to your doctor about them immediately since treatment at this stage is considered more effective.

In addition to finger clubbing, ACS notes that symptoms may include a cough that does not go away or gets worse, coughing up blood or rust-colored phlegm, chest pain that worsens with deep breathing, a hoarse voice, loss of appetite or unexplained weight loss, shortness of breath, fatigue, chronic infections such as bronchitis and pneumonia, and wheezing. In advanced cancer cases, patients may additionally experience bone pain, nervous system problems, jaundice, or swelling of the lymph nodes.

Clubbing is also caused by these other conditions.

Finger clubbing can be a sign of lung cancer with or without additional symptoms. However, it has also been linked to a range of other health problems that can also reduce the amount of oxygen in the blood. Some of these include non-cancerous lung conditions, such as chronic lung infections, lung abscess, and interstitial lung disease, reports Mount Sinai.

Additionally, finger clubbing can be caused by certain heart conditions, including congenital heart disease, pulmonary fibrosis, and endocarditis—an infection in the lining of the heart chambers or valves. Other conditions which have been linked to finger clubbing include celiac disease, liver cirrhosis, Graves disease, overactive thyroid, and dysentery. Certain other forms of cancer can cause clubbing, such as that of the liver, gastrointestinal tract, and Hodgkin lymphoma.

Given its wide range of possible causes, it's important to speak with your doctor if you can't see a diamond gap between your fingernails. However, "people shouldn't freak out if they have clubbing," Presser told Health. "If you do notice this change, make sure you talk to your doctor about some of the potential possibilities that you want to rule out."

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