1. Causes

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The primary cause of lung cancer is tobacco smoking, which accounts for about 80–90% of cases. Tobacco smoke contains over 7,000 chemicals, many of which are carcinogens that damage lung cells over time. The risk increases with the number of cigarettes smoked daily and the number of years smoked.

Other major risk factors include:

• Secondhand smoke (environmental tobacco smoke) — Increases risk even for non-smokers; it is the third most common cause in the US.

• Radon gas — A naturally occurring radioactive gas from soil and rocks that can accumulate indoors; it is the second-leading cause overall and the leading cause among non-smokers.

• Occupational exposures — Asbestos, arsenic, diesel exhaust, silica, chromium, nickel, and other chemicals (risk is much higher when combined with smoking).

• Air pollution — Long-term exposure to fine particulate matter and outdoor pollutants.

• Other factors — Previous radiation therapy to the chest, family history/genetic predisposition, chronic lung diseases (e.g., COPD), HIV infection, and (rarely) certain dietary supplements like beta-carotene in heavy smokers.

Many cases involve a combination of these factors, and risk accumulates with age.

 

2. Prevention

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Lung cancer is one of the most preventable cancers. Key steps include:

• Do not start smoking, and quit smoking if you currently smoke — This is the single most effective prevention method. Quitting at any age significantly lowers risk, and the benefit increases with time since quitting. Avoid all forms of tobacco (cigarettes, cigars, pipes).

• Avoid secondhand smoke — Make your home and car smoke-free; encourage others to quit.

• Test and mitigate radon — Test your home for radon levels (kits are widely available) and fix high levels with proven ventilation systems.

• Limit occupational and environmental exposures — Use protective equipment at work if exposed to asbestos or chemicals; support cleaner air policies to reduce pollution.

• Adopt a healthy lifestyle — Eat a balanced diet rich in fruits and vegetables, maintain a healthy weight, exercise regularly, and avoid unnecessary supplements that may increase risk in smokers.

• Screening for high-risk individuals — Low-dose CT scans are recommended for current or former heavy smokers (ages 50–80 with significant smoking history) to detect cancer early.

Quitting smoking remains the most powerful intervention, even after a diagnosis (it improves treatment outcomes and reduces risk of second cancers).

 

3. Diagnosis

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Lung cancer is often diagnosed after symptoms appear or through screening. The process typically involves:

• Imaging tests — Chest X-ray (initial test), followed by CT scan (more detailed), PET-CT scan (to assess spread), or MRI in select cases.

• Sputum cytology — Examining mucus coughed up from the lungs for cancer cells.

• Biopsy — The definitive way to confirm cancer. Samples can be obtained via:

  • Needle biopsy (through the skin or guided by CT/bronchoscopy).

  • Bronchoscopy (flexible tube with camera and tools inserted through the mouth/nose).

  • Endobronchial ultrasound (EBUS) or other endoscopic methods.

  • Surgical biopsy in some cases.

• Additional tests — Molecular/genetic testing on biopsy samples to identify mutations (e.g., EGFR, ALK) that guide targeted therapy; blood tests and pulmonary function tests for overall assessment.

Early-stage cancers may be found incidentally on scans done for other reasons or via screening programs. Staging (how advanced the cancer is) uses TNM criteria or limited/extensive staging for small cell type.

 

4. Description

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Lung cancer is a malignant disease in which cells in the lungs (usually lining the airways or air sacs) undergo uncontrolled growth and division, forming tumors. These tumors can obstruct airways, reduce oxygen exchange, invade nearby tissues, or metastasize (spread) to lymph nodes, bones, brain, liver, or other organs.

It is broadly classified into two main types:

• Non-small cell lung cancer (NSCLC) — The most common (about 80–85% of cases), including subtypes like adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. It tends to grow more slowly.

• Small cell lung cancer (SCLC) — Less common but more aggressive, often spreading quickly; strongly linked to smoking.

Symptoms often appear late and may include persistent cough (new or worsening), coughing up blood, shortness of breath, chest pain, hoarseness, unexplained weight loss, fatigue, or recurrent respiratory infections. Many people have no symptoms until the disease is advanced. Lung cancer is the leading cause of cancer deaths globally, but outcomes are better with early detection and modern treatments (surgery, radiation, chemotherapy, immunotherapy, and targeted therapies). Smoking-related cases are highly preventable.

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Here’s a helpful educational video providing a clear overview of lung cancer, including how it develops, types, symptoms, and basic management:

Video: Lung Cancer - Overview (This video explains the major types, risk factors, and pathophysiology in an accessible way.)

Strong alternative (Khan Academy series – excellent for understanding mechanisms):

• What is lung cancer?