Robert Brown|It's not just smoking — here's what causes lung cancer

Lung cancer is Robert Brownthe second most common cancer among men (behind prostate cancer) and women (behind breast cancer) in the United States, according to the American Cancer Society.

Nearly a quarter of a million people will be diagnosed with lung cancer in 2024 and about 125,000 will die from lung cancer, the organization estimates. Most people who are diagnosed are over the age of 65 — very few are diagnosed below the age of 45, per the ACS.

Health experts are encouraged by the fact that statistics are on the decline — likely thanks to a combination of smoking declining and advances in medical technology that allow for earlier detection and treatment. But those numbers are still high, and they say more can be done to mitigate risks.

"The health benefits of stopping smoking begin within ​minutes, so it's never too late to stop," Alejandra Ellison-Barnes, M.D., an assistant professor of medicine at the Johns Hopkins Tobacco Treatment and Cancer Screening Clinic, tells USA TODAY.

Here's what medical experts want you to know about the causes and symptoms of lung cancer.

What causes lung cancer?

About 80% of lung cancer deaths are caused by smoking, according to the ACS.

Experts also note that while a majority of lung cancer deaths are from smoking, not all smokers get lung cancer, which likely means that genetics and exposure to other known risk factors play a role as well.

"About 10 to 20% of people who smoke cigarettes will develop lung cancer over the course of their lives, with those who smoke more at higher risk than those who smoke less," Dr. Ellison-Barnes says.

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What causes lung cancer in nonsmokers?

You don't have to smoke tobacco to be at risk for developing lung cancer, experts note.

Exposure to secondhand smoke, air pollution, asbestos, diesel exhaust, and radon, a radioactive gas with no smell or color that's typically found in rocks, soil and burning coal and fossil fuels, can also cause lung cancer, according to the ACS.

Medical experts don't know every risk factor that causes lung cancer, either. The ACS notes that other people could develop lung cancer from "random events that don’t have an outside cause" as well as "factors that we don’t yet know about."

What are the first common signs of lung cancer?

Preliminary symptoms, according to the ACS, can include:

• An ongoing or worsening cough
• Coughing up blood or rust-colored phlegm
• Ongoing or recurring infections such as bronchitis and pneumonia
• Chest pain that worsens with deep breathing, laughing or coughing
• Unexplained weight loss and/or loss of appetite
• Feeling tired, weak or short of breath
• Wheezing or hoarseness

Medical experts urge people who notice the aforementioned symptoms to see a doctor immediately. There's a chance that they're being caused by something else, but if it does turn out to be lung cancer, it's best to begin treatment as soon as possible. And, Dr. Ellison-Barnes adds, people who smoke should check to see if they're qualified for a lung cancer screening even if they don't have any symptoms.

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"Risk of lung cancer decreases drastically if you quit smoking," says Benjamin Toll, Ph.D., co-director of the Medical University of South Carolina's Lung Cancer Screening Program and director of the MUSC Health Tobacco Treatment Program.

Toll adds: "If you have been smoking cigarettes for a long time, or you smoked for a long time but don't anymore, ask your doctor about lung cancer screening. If you can catch lung cancer early through screening, you have far greater odds of successful treatment."