Lung Cancer: Causes, Prevention, and Who Should Get a Screening CT Scan

Lung cancer is the leading cause of cancer death in the world. The main reason is timing: it usually causes few symptoms early on, so it is often found only after it has grown or spread, when it is much harder to cure. Two things can change that: avoiding what causes it, and screening people at higher risk so the cancer is found at an early stage.

Key Takeaways

• Worldwide, lung cancer is the most common cancer and the leading cause of cancer death, with an estimated 2.5 million new cases and 1.8 million deaths in 2022.
• Tobacco is the main cause. WHO attributes 60–70% of preventable lung cancer cases to smoking, and in the United States smoking is linked to about 80% of lung cancer deaths. Secondhand smoke, radon, air pollution, and workplace exposures such as asbestos also play a role.
• Quitting lowers your risk every year, and after 10 to 15 years your added risk is about half what it was. It is never too late.
• Yearly low-dose CT screening is recommended for adults aged 50 to 80 with a 20 pack-year smoking history who currently smoke or quit within the past 15 years. A chest X-ray is not good enough to find small cancers.
• In Pakistan, lung cancer is among the leading causes of cancer death, especially in men, and cough is often assumed to be TB, which can delay the right tests.

Why Is Lung Cancer So Deadly?

Lung cancer often causes no symptoms until it is large or has spread. By then it is harder to treat. The picture is much better when it is found early, which is why screening matters for the people most likely to develop it.

What Causes Lung Cancer?

• Smoking is the leading cause. The more you have smoked, and the longer, the higher your risk. Since many lung cancers occur in people who smoke, the most important step is never to start, and if you smoke, to quit as soon as you can.
• Secondhand smoke: breathing other people's smoke also causes lung cancer.
• Radon: a naturally occurring radioactive gas that can build up in buildings. It can cause lung cancer in people who have never smoked, and the risk is higher for people who smoke.
• Air pollution: living with higher levels of air pollution raises risk.
• Workplace exposures: substances such as asbestos raise risk, again more so in people who smoke.

Quitting helps: lung cancer risk starts falling with each smoke-free year, and 10 to 15 years after quitting your added risk is about half. Quitting also lowers the risk of many other cancers and of heart and lung disease.

Who Should Get Screened?

The US Preventive Services Task Force recommends a yearly low-dose CT scan of the chest for people who meet all of these:

• Aged 50 to 80
• A smoking history of 20 pack-years or more
• Currently smoke, or quit within the past 15 years

Screening usually stops once you have been smoke-free for more than 15 years, or if a health problem would limit your life expectancy or your ability to have curative surgery. Newer American Cancer Society guidance keeps the age and pack-year criteria but drops the "years since quitting" limit, so people who quit long ago may still qualify. Ask your doctor which approach they use.

What is a pack-year?

A pack-year measures how much you have smoked over your life. Multiply the packs per day by the number of years you smoked. One pack a day for 20 years is 20 pack-years. Half a pack a day for 40 years is also 20 pack-years.

Why CT and not a chest X-ray?

A plain chest X-ray can miss small cancers. In a large US trial, yearly low-dose CT screening reduced lung cancer deaths by 20% compared with chest X-ray screening. Modern low-dose CT also uses much less radiation than older scans, so a yearly scan is considered safe for people who qualify.

Screening is for people without symptoms. If you have a cough that won't go away, cough up blood, or lose weight without trying, see a doctor promptly for a proper evaluation instead of waiting for a screening slot.

What If the Scan Shows a Spot?

The CT looks for spots, called nodules. Many people will have a clear scan. Some will have a nodule that needs a closer look, and a nodule does not always mean cancer. Depending on its size, shape, and location, doctors may:

• Watch it with repeat CT scans
• Take a sample (biopsy)
• Remove the affected part with surgery

Following up on a spot can feel stressful, but if it turns out to be cancer, finding it early gives you a much better chance of cure. A normal first scan doesn't end screening: new spots can appear with time, so keep getting scanned every year for as long as you are eligible. Ask your lung doctor if you have questions.

Why This Matters in Pakistan

Lung cancer is a major cause of cancer death here, especially in men. IARC's estimates for Pakistan put lung cancer second among causes of cancer death overall and first among men, with roughly 7,600 to 9,500 deaths a year depending on the estimate. Tobacco is a big driver: about one in five adults uses tobacco (31.8% of men), including cigarettes and smokeless products. Because lung cancer is often found late, it matters that early symptoms such as a persistent cough or breathlessness are commonly assumed to be TB. The Pakistan Medical Association says this delays proper cancer workups by months, and it also says a large share of urban lung cancers occur in people who never smoked, pointing to air pollution (these are the PMA's statements, not independently verified here). If a cough or chest symptom doesn't improve with treatment, ask your doctor whether other causes need to be ruled out. We could not find an established national lung cancer screening programme in Pakistan, so ask your doctor whether a low-dose CT is available to you and appropriate for your risk.

Frequently Asked Questions

I quit smoking years ago. Do I still need screening? It depends on your age, pack-years, and how long ago you quit. Under USPSTF criteria, screening can stop after 15 years smoke-free, while newer American Cancer Society guidance has no such cutoff. Talk to your doctor.

Is the radiation from a yearly CT scan dangerous? Low-dose CT uses much less radiation than older scans. For people who meet the criteria, the benefit of finding cancer early is considered to outweigh that small risk.

If I have a nodule, do I have cancer? Not necessarily. Many nodules are not cancer. Your doctor will decide whether to watch it with repeat scans, take a biopsy, or remove it.

Can people who never smoked get lung cancer? Yes. Secondhand smoke, radon, air pollution, and workplace exposures can all cause it.

Is a chest X-ray enough to check for lung cancer? No. A chest X-ray can miss small cancers, which is why low-dose CT is used for screening.

Take the Next Step

Avoiding smoking and getting the right screening at the right time can save lives. If you smoke and want to quit, or you think you may qualify for lung cancer screening, book a consultation with a Dr. Smart physician, and use the Dr. Smart GO app to keep track of your screening schedule and results.

This article is for informational purposes and does not replace professional medical advice. Consult a qualified healthcare provider to find out whether lung cancer screening is right for you.