Finger Clubbing: A Sign of Early-Stage Lung Cancer
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The Weirdest Early Warning Sign of Lung Cancer

The Weirdest Early Warning Sign of Lung Cancer
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Published on June 27, 2025
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Most lung cancers don’t cause symptoms until they’ve spread. But when people do have symptoms, a persistent cough, unexpected weight loss, and shortness of breath are the most common ones.

One unusual symptom that isn’t as easy to identify as lung cancer is finger clubbing. This upside-down spoon-like swelling in the tops of the fingers affects a small percentage of people with lung cancer, but it’s worth paying attention to because clubbing can be one of the first signs of this disease.

What Is Finger Clubbing?

Finger clubbing is a change in the appearance and feel of the fingernails or toenails. The nail widens and bulges at the cuticle.

“The finger looks kind of like an upside-down spoon shape, rather than having a natural concave curve at the cuticle,” says Bryan Andrew Faller, MD, director of cancer research at Missouri Baptist Medical Center in St. Louis.

Affected nails also:

  • Feel warm
  • Get soft and spongy
  • Turn red
  • May feel painful

With finger clubbing in early-stage lung cancer, the nail changes occur so slowly that they aren’t noticeable. “With a lot of patients I meet with lung cancer, I look at their fingers and they have [finger clubbing] and they didn't even know it,” says Dr. Faller.

Finger clubbing isn’t dangerous. It’s mainly a cosmetic issue, and the nails should return to their original size and shape once the cancer is treated, says Faller, although occasionally finger clubbing remains after the cancer is cured.

Finger clubbing is not always caused by lung cancer — it can occur alongside many other conditions, such as celiac disease or Graves’ disease. Speak with your doctor if you think you have finger clubbing to determine the cause.

Schamroth Window Test

Often, doctors can diagnose clubbing just from looking at the fingers. The Schamroth window test is a way to confirm the diagnosis in more subtle cases, says Faller.

In this test, the person places their two index fingers together, nail to nail, forming a heart shape. There should be a small, diamond-shaped window between the cuticles of the fingers. In people with finger clubbing, the fingers will lie flat against each other and no window is visible.

Graphic titled Schamroth Window Test. Illustrated points include no finger clubbing and finger clubbing. A diamond-shaped 'window' or space can be seen when fingers are not clubbed. When there is finger clubbing, this window is missing. Everyday Health
Everyday Health.

Why Does Lung Cancer Cause Finger Clubbing?

Experts don’t know exactly how lung cancer causes finger clubbing, but they have some ideas. One of the leading theories is that a drop in oxygen triggers the release of a protein called vascular endothelial growth factor (VEGF). VEGF causes blood vessels to expand and fluid to build up under the nails, which makes them swell.

Finger clubbing is not a very common symptom of lung cancer. According to an older study, approximately 1 percent of people with lung cancer develop clubbed nails. No newer research is available.

Other Early Symptoms of Lung Cancer

Detecting and treating lung cancer early can improve survival. These are some other symptoms to watch for:

  • A persistent cough that isn’t related to another illness and that doesn’t go away
  • Coughing up blood
  • Shortness of breath
  • Chest pain that gets worse when you breathe deeply, cough, or laugh
  • A hoarse, raspy voice
  • Bronchitis, pneumonia, or emphysema that doesn’t improve
  • Unexplained weight loss
  • Pain in the bones, especially in the shoulders, arms, or neck

These can also be symptoms of many other conditions. Only a doctor can confirm the diagnosis.

When to See a Doctor

See a doctor for clubbing or other lung cancer symptoms. “It’s important to get checked out, especially if you have risk factors for lung cancer,” Faller says. You can start with your primary care doctor, who will likely do a chest X-ray or CT scan.

Risk factors for lung cancer include:

  • Smoking or exposure to secondhand smoke
  • Exposure to radon, which can seep into buildings or homes through the soil
  • Exposure to carcinogens at work or chemicals in the home
  • Radiation to the chest, such as for breast cancer
  • Family history of lung cancer

Other Causes of Finger Clubbing

Although lung cancer is the most common cause of clubbing, it’s not the only cause. The symptom is also related to these conditions:

The Takeaway

  • ​Clubbing is an upside-down spoon-like shape in the fingernails or toenails. Lung cancer is one of many possible causes, and only a small percentage of people with lung cancer will develop this symptom.
  • Finger clubbing suggests an underlying health problem, which may or may not be lung cancer. Speak with your doctor if you are experiencing finger clubbing to determine the cause.
  • Your nails may gradually return to normal, but it’s also possible that the finger clubbing will remain.

Resources We Trust

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Signs and Symptoms of Lung Cancer. American Cancer Society. February 27, 2025.
  2. Burcovschii S et al. Nail Clubbing. StatPearls. September 24, 2022.
  3. Nail Clubbing. Cleveland Clinic. November 23, 2022.
  4. Rajagopalan M et al. Evaluation of Clubbing. BMJ Best Practice. June 25, 2024.
  5. Izumi M et al. Incidence of Hypertrophic Pulmonary Osteoarthropathy Associated With Primary Lung Cancer. Respirology. June 21, 2010.
  6. 7 Signs of Lung Cancer You Should Know. Lung Cancer Foundation of America.
  7. Lung Cancer Risk Factors. American Cancer Society. January 29, 2024.
  8. Clubbed Fingers. Cleveland Clinic. August 4, 2022.
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Tawee Tanvetyanon

Medical Reviewer

Tawee Tanvetyanon, MD, MPH, is a professor of oncologic sciences and senior member at H. Lee Moffitt Cancer Center and Morsani College of Medicine at the University of South Florida in Tampa. He is a practicing medical oncologist specializing in lung cancer, thymic malignancy, and mesothelioma.

A physician manager of lung cancer screening program, he also serves as a faculty panelist for NCCN (National Comprehensive Cancer Network) guidelines in non-small cell lung cancer, mesothelioma, thymoma, and smoking cessation. To date, he has authored or coauthored over 100 biomedical publications indexed by Pubmed.

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Stephanie Watson

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Stephanie Watson is a freelance health writer who has contributed to WebMD, AARP.org, BabyCenter, Forbes Health, Fortune Well, Time, Self, Arthritis Today, Greatist, Healthgrades, and HealthCentral. Previously, she was the executive editor of Harvard Women’s Health Watch and Mount Sinai’s Focus on Healthy Aging. She has also written more than 30 young adult books on subjects ranging from celebrity biographies to brain injuries in football.
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