When you hear the word cancer, there are many things you might think to check before your fingernails.

However, you could be missing a vital warning sign by not examining them regularly, as they could provide a clue that something is seriously wrong.

The American Cancer Society says that lung cancer is the second-most common cancer in men and women in the US.

It's often not discovered until it's too late, as they are often respiratory and mixed up with coughs and colds which causes confusion.

Many of us know to keep an eye out for wheezing, any persistent coughs and breathlessness, as well as blood in phlegm.

However, a lesser-known sign can show up on our hands.

If you're glancing at them now, what should you be looking for?

You need to monitor for any swelling in the fingers and changes to the nail shape.

Known as finger clubbing, it's often a symptom of something else rather than a standalone disease.

Experts think this happens because lung tumors release chemicals or hormones which inflame the bones in the fingers.

One patient, from the UK, reported that they had no other symptoms of lung cancer besides finger clubbing when they were diagnosed.

Brian Gemmell told The Mirror: "Go and see your doctor—that's what a GP is for."

"Go as soon as you can," he insisted, and said he was 'feeling healthy' when he received the shock diagnosis.

Brian added: "I wasn’t coughing up blood, I wasn’t breathless. My one and only symptom was clubbing of the fingers, where all your fingers swell up and when you put your fingers together you can’t see a diamond.

"That was my only symptom. Straightaway, my GP had an idea of what it was. He sent me straight for a chest X-ray and referred me to a respiratory consultant."

The test Brian is referring to involves pressing two opposing fingers against each other to check for a diamond shape.

If you don't see a small diamond, it could be an indication of finger clubbing.

A 2012 study by Dr Malay Sarkar, an India-based lung cancer specialist, found that lung cancer is the primary cause of finger clubbing.

Shockingly, it is linked to almost 90 percent of cases, while nail clubbing affects around five to 15 percent of people with lung cancer.

However, Cancer Research UK adds that not everyone with finger clubbing will have lung cancer.

Dr Helen Piercy also told the Mirror: "If you notice any signs or symptoms that concern you, see your GP.

"First phone for an appointment. You will be assessed. You will be invited in, if you need to be seen face-to-face. Don't be afraid. Pick up the phone."