Lung Cancer: Types, Causes, Symptoms, Stages, and Treatment

What Is Lung Cancer?

Lung cancer develops when cells in the lungs grow too quickly and do not stop growing. These extra cells can form tumors, which may block the airways and make it hard for the lungs to work properly. Lung cancer is the main cause of cancer deaths in both men and women around the world. According to the World Health Organization (WHO), more than 1.8 million people die from it every year.

In the United States alone, approximately 229,410 new cases are diagnosed every year, according to the American Cancer Society (ACS).

Lung cancer most commonly begins in the bronchi (large airways), bronchioles (smaller airways), or alveoli (air sacs). Once a tumor forms, it can spread or metastasize to nearby lymph nodes, the other lung, or distant organs such as the brain, liver, or bones.

What Are the Types of Lung Cancer?

• Non-Small Cell Lung Cancer (NSCLC): This is the most common type. It makes up about 80% to 85% of all lung cancer cases. This cancer usually grows and spreads more slowly than small-cell lung cancer.

There are three main subtypes:

• Adenocarcinoma: The most common subtype, often found in the outer areas of the lungs. It is the most common type in non-smokers.

• Squamous Cell Carcinoma: Usually arises near the central bronchi and is strongly associated with smoking.

• Large Cell Carcinoma: It can grow in any part of the lung and may spread rapidly to other parts of the body.

• Small Cell Lung Cancer (SCLC): This accounts for about 10% to 15% of lung cancers. It is also called "oat cell cancer" due to its appearance under a microscope. SCLC grows rapidly, spreads early, and is almost always associated with heavy cigarette smoking. Because it spreads fast, it is typically found after it has already metastasized.

• Other Lung Tumors: Rarer forms include carcinoid tumors (slow-growing neuroendocrine tumors), pleural mesothelioma (cancer of the lung lining, linked to asbestos), and pulmonary lymphomas.

What Are the Causes and Risk Factors of Lung Cancer?

These include:

• Smoking: This is the leading cause of lung cancer, responsible for about 80 to 85% of cases. People who smoke are 15 to 30 times more likely to get cancer than people who don’t smoke. The more and longer they smoke, the higher the risk. Pipe and cigar smoking also increases risk, though slightly less than cigarettes.

• Other Causes:

  • Radon Gas: Radon gas comes from soil and rocks. It is considered as the second biggest cause of lung cancer in the US, causing approximately 21,000 deaths per year (US EPA).

  • Secondhand Smoke: Exposure to others' cigarette smoke causes more than 7,300 lung cancer deaths annually in the US.

  • Occupational Exposures: Carcinogens such as asbestos, diesel exhaust, and crystalline silica can increase the risk.

  • Air Pollution: Long-term exposure to pollution can harm the lungs.

  • Family History: Having a family history can increase your risk.

  • Prior Radiation Therapy: People who received chest radiation for other cancers face an increased risk.

What Are the Symptoms of Lung Cancer?

Most people with early-stage lung cancer have no symptoms at all. When symptoms appear, they are often mistaken for a common cold, bronchitis, or other respiratory infections.

• Early Symptoms:

  • A persistent cough that does not go away or worsens over time.

  • Shortness of breath or new-onset wheezing.

  • Hoarseness or voice changes.

  • Coughing up blood (hemoptysis), even a small amount.

  • Chest pain (increasing with deep breathing or coughing).

• Advanced or Late-Stage Symptoms: As lung cancer spreads, additional symptoms may appear:

  • Unexplained weight loss and loss of appetite.

  • Persistent fatigue and weakness.

  • Bone pain (more in the back or hips).

  • Headaches or dizziness (when cancer has spread to the brain).

  • Swelling of the face, neck, or arms (due to blocked veins).

  • Yellowing of the skin or eyes (jaundice, when cancer has spread to the liver).

• Paraneoplastic Symptoms: Some lung cancers produce hormones or other substances that cause symptoms unrelated to the lungs themselves, including:

  • High blood calcium (hypercalcemia) causes nausea, confusion, and constipation.

  • Cushing's syndrome (elevated cortisol).

  • Clubbing of the fingers or toes.

What Are the Stages of Lung Cancer?

1. NSCLC Staging:

Stage	What It Means	5-Year Survival Rate
Stage IA	Tumor measuring 1.18 inches or less, confined to the lung.	77 to 92%
Stage IB	Tumor measuring more than 1.18 inches but 1.57 inches or less, confined to the lung.	68%
Stage IIA	Tumor measuring more than 1.57 inches but 1.96 inches or less confined to the lung.	60%
Stage IIB	Tumor measuring more than 1.96 inches or spread to nearby lymph nodes.	53%
Stage IIIA	Cancer has spread to the chest lymph nodes on the same side.	36%
Stage IIIB	Cancer has spread to the lymph nodes on the other side.	26%
Stage IV	Spread to the other lung or distant organs.	7 to 10%

2. SCLC Staging (Limited vs. Extensive):

• Limited Stage: In this stage, the cancer is in one lung and nearby lymph nodes. About 1 in 3 people find it at this stage.

• Extensive Stage: In this stage, the cancer has spread throughout the lungs or to other organs. Most cases are found at this stage.

How Is Lung Cancer Diagnosed?

Lung cancer is diagnosed using several procedures:

1. Imaging Tests: The initial test will be a chest X-ray. If further details are needed, a CT scan will be performed. In case there is an indication that the cancer has metastasized, a PET scan is recommended.

2. Sputum Cytology: Examining phlegm under a microscope for cancer cells. Useful when the tumor is near the central airways.

3. Bronchoscopy: A special procedure that helps in examining the lungs and airways with the help of a tiny tube that has a camera.

4. Needle Biopsy (CT-Guided): A needle biopsy uses a needle inserted through the chest to obtain a small tissue sample from the lung.

5. Thoracoscopy or Mediastinoscopy: Surgical procedures to sample lymph nodes and assess spread.

6. Molecular Testing: Once cancer is confirmed, tumor tissue is tested for genetic mutations (EGFR, KRAS, ALK, ROS1, BRAF, PD-L1) to guide targeted therapy decisions.

Lung Cancer Screening: Who Should Be Screened?

Annual low-dose CT (LDCT) screening is recommended for adults who meet all of the following criteria:

1. Aged 50 to 80 years.

2. Still smoke or quit in the last 15 years.

3. Have a smoking history of at least 20 pack-years (like 1 pack a day for 20 years or 2 packs a day for 10 years).

Studies show LDCT screening can lower lung cancer deaths by about 20% in high-risk people. Screening is not recommended for people with no smoking history or those with serious health conditions that would prevent treatment.

How Is Lung Cancer Treated?

Treatment depends on the cancer type, stage, and the person’s health. A team of doctors works together to choose the best plan.

1. Surgery: Surgery is the main treatment for early-stage NSCLC. The goal is to remove the tumor and some surrounding healthy tissue.

Common surgeries include:

• Lobectomy: One of the lobes of the lung is removed (most common).

• Segmentectomy or Wedge Resection: Removing a smaller portion of the lung for very early tumors.

• Pneumonectomy: Removing an entire lung (less common, used for central tumors).

2. Radiation Therapy: Radiation therapy uses strong X-rays to kill cancer cells. SBRT (stereotactic body radiotherapy) gives strong, focused treatment in a few sessions, often for early cancer when surgery is not possible.

3. Chemotherapy: Chemotherapy uses drugs (usually given intravenously) to kill cancer cells throughout the body. It is often combined with radiation for locally advanced NSCLC and is the primary treatment for SCLC. Common regimens include platinum-based combinations (Carboplatin or Cisplatin with Paclitaxel or Pemetrexed).

4. Targeted Therapy: For patients with specific genetic mutations, targeted drugs block the proteins that allow cancer cells to grow:

• EGFR Inhibitors: Osimertinib, Erlotinib.

• ALK Inhibitors: Alectinib, Crizotinib.

• KRAS Inhibitors: Sotorasib for KRAS G12C mutation.

• ROS1 Inhibitors: Repotrectinib, approved by the FDA in 2023.

5. Immunotherapy: The immunotherapy will help your body's defense mechanism recognize cancer cells. Some drugs, such as Pembrolizumab and Nivolumab, have contributed to the longer life spans of patients with advanced stages of NSCLC. Pembrolizumab can also be used initially if the patient has high PD-L1 levels.

Which Medical Conditions Can Mimic Lung Cancer?

Several conditions present with similar symptoms should be ruled out:

• Tuberculosis (TB).

• Chronic obstructive pulmonary disease (COPD).

• Pneumonia.

• Pulmonary embolism.

• Gastroesophageal reflux disease (GERD).

• Benign lung nodules or lung abscess.

A CT scan and biopsy are the definitive tests to distinguish lung cancer from these conditions.

When Should You See a Doctor?

See a doctor promptly if you experience any of the following:

• A cough that lasts over 8 weeks or keeps getting worse.

• Coughing up blood or rust-colored sputum.

• New shortness of breath not explained by asthma or COPD.

• Chest pain that worsens with cough or breathing.

• Unexplained weight loss (more than 8 to 11 pounds over a few weeks).

• Hoarseness lasting more than 2 to 3 weeks without a clear cause.

If you are 50 to 80 and smoke now or used to smoke a lot, ask your doctor about yearly LDCT lung cancer screening.

Conclusion

Lung cancer signs can mimic common breathing problems, such as cough, shortness of breath, or chest pain. If they last more than 8 weeks and do not get better, see a doctor. Early-stage lung cancer can be treated. Stage 1 survival is over 77%. Screening helps find it early before symptoms start. If you are experiencing persistent respiratory symptoms, consult a lung doctor for a detailed evaluation without the wait.

Key Takeaways

• Lung cancer is the top cancer killer in the world, causing over 1.8 million deaths each year.

• NSCLC makes up about 80 to 85% of lung cancer cases. SCLC makes up 10 to 15%.

• Most people have no symptoms in the early stages; a persistent cough lasting more than 8 weeks is the most common warning sign.

• When caught at stage I, the 5-year survival rate ranges from 70% to 90%, depending on the sub-stage.

• Low-dose CT (LDCT) screening is recommended for adults aged 50 to 80 with a significant smoking history.