What is Lung Cancer?

About Cancer Types Stages Causes Symptoms Screening Treatment

What is Lung Cancer?

The lungs are an essential part of the respiratory system. The respiratory system consists of a pair of lungs that also have different parts. The right lung has three lobes, and the left lung has two. A thin layer called the pleura protects the lungs. Cells in the lungs do tend to change and can grow or stop behaving normally. Some of these cells can grow into benign, non-cancerous tumors or malignant tumors.

These cells can destroy the nearby tissue and can also spread to other parts of the body, causing lung cancer. Lung cancers can be primary and secondary, depending on the location that it starts. Primary tumors in the lungs start locally, and secondary ones start in another part of the body and spread to the lungs.

It is also further divided into non-small cell lung cancer and small cell lung cancer, depending on the appearance of the cancer cells under the microscope.

Types of Lung Cancer

Lung cancer is primarily classified into two main types: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Understanding the type helps guide treatment and prognosis.

Non-Small Cell Lung Cancer (NSCLC)

NSCLC accounts for 80–85% of lung cancer cases. Its main subtypes include:

Adenocarcinoma: The most common form, originating in mucus-producing epithelial cells. It affects both smokers and non-smokers and is more common in women and younger individuals.
Squamous Cell Carcinoma: Begins in the flat cells lining the airways, often linked to smoking, and typically found near the central lung.
Large Cell Carcinoma: Can occur anywhere in the lung and grows rapidly. A subtype, large cell neuroendocrine carcinoma (LCNEC), behaves similarly to SCLC.
Other Rare Subtypes: Includes adenosquamous and sarcomatoid carcinoma.

Small Cell Lung Cancer (SCLC)

SCLC makes up 10–15% of lung cancers. It grows and spreads quickly, often diagnosed after it has metastasized. While it responds well to chemotherapy and radiation, recurrence is common.

Other Lung Tumors

Lung Carcinoid Tumors: Slow-growing and rare, accounting for less than 5% of lung tumors.
Other Rare Tumors: Includes adenoid cystic carcinomas, lymphomas, sarcomas, and benign tumors like hamartomas.

Metastatic Cancer to the Lungs

Cancers from other organs (e.g., breast, pancreas, kidney) can spread to the lungs. These are treated based on their original site, not as lung cancer. American Cancer Society - What is Lung Cancer?

Stages of Lung cancer

The stage of a cancer tells you how big it is and whether it has spread. Doctors use the TNM or number staging systems to stage lung cancer. They might also use limited and extensive stages to stage small cell lung cancer.

Stages of non-small cell lung cancer

Stage 0: “In situ,” meaning “in place.” The tumors have not grown into nearby tissues, and there are no signs of cancer outside the lung.
Stage 1: Tumors are small (less than 5 centimeters wide) and have not spread to any nearby lymph nodes. In most cases, stage 1 lung cancer doesn’t produce any noticeable symptoms.
Stage 2: Tumors are still small (less than 7 centimeters wide) but have started to spread to local lymph nodes or other nearby structures. Like stage 1 lung cancer, stage 2 lung cancer typically doesn’t cause any noticeable symptoms.
Stage 3: Cancers have spread to the lymph nodes in the center of the chest or other structures outside the lung. By the time lung cancer reaches stage 3, it’s more likely to produce noticeable symptoms.
Stage 4: Cancer spreads to other lung, fluid around lungs, or distant organs. Symptoms may include severe cough, blood in phlegm, or neurological issues.

Stages of Small Cell Lung Cancer (SCLC)

Limited Stage: Confined to one side of the chest and nearby lymph nodes.
Extensive Stage: Spread beyond the lung to other parts of the body.

Moffitt Cancer Center - Lung Cancer Stages

Causes of Lung Cancer

Smoking tobacco: The leading cause of lung cancer.
Workplace exposure to harmful substances: Asbestos, Silica, Diesel exhaust fumes
Air pollution: Contributes to around 8% of lung cancer cases in the UK; risk depends on exposure levels.
Previous lung diseases: COPD (emphysema, chronic bronchitis), Pneumonia, Idiopathic pulmonary fibrosis (IPF)
Radon gas exposure: Naturally occurring radioactive gas; risk is higher in certain UK regions and increases with smoking.
Family history
High-dose beta-carotene supplements: May increase lung cancer risk in current or former smokers.

Cancer Research UK - Lung Cancer Risks & Causes

Symptoms of Lung Cancer

The main symptoms of lung cancer include:

A cough that does not go away after 3 weeks
A long-standing cough that gets worse
Chest infections that keep coming back
Coughing up blood
An ache or pain when breathing or coughing
Persistent breathlessness
Persistent tiredness or lack of energy
Loss of appetite or unexplained weight loss

Less common symptoms of lung cancer include:

Changes in the appearance of your fingers, such as becoming more curved or their ends becoming larger (this is known as finger clubbing)
Difficulty swallowing (dysphagia) or pain when swallowing
Wheezing
A hoarse voice
Swelling of your face or neck
Persistent chest or shoulder pain

NHS - Lung Cancer Symptoms

Screening & Diagnosis

Currently, low-dose CT (LDCT) scans are used to screen individuals at high risk of lung cancer, especially those with a history of smoking. These scans can detect abnormal lung areas early, often before symptoms appear. Unlike chest X-rays, annual LDCT screenings have been shown to reduce lung cancer deaths in high-risk groups. American Cancer Society - Lung Cancer Detection

The US Preventive Services Task Force (Task Force) recommends yearly lung cancer screening with LDCT for people who:

Have a 20 pack-year or more smoking history, and
Smoke now or have quit within the past 15 years, and
Are between 50 and 80 years old.

A pack-year is smoking an average of one pack of cigarettes per day for one year. For example, a person could have a 20 pack-year history by smoking one pack a day for 20 years or two packs a day for 10 years. CDC - Lung Cancer Screening

Chest X-ray

A chest x-ray is particularly used in emergency diagnosis and treatment as it is a fast method. This method of screening is most commonly used to evaluate symptoms like shortness of breath, chest pain and persistent cough.

Sputum cytology

Sputum cytology is a kind of diagnostic test that is conducted wherein a sample of the mucus that contains blood is taken and view under a microscope to check for the presence of abnormal cells.

Common diagnostic methods for lung cancer:

Computed tomography (CT): X-ray machines project a cross-sectional view of the lungs on a computer
Positron emission tomography (PET) scan: Helps understand if cancer has spread to other parts of the body
Bronchoscopy: A tube passes through the nose or mouth and into the lungs to check for tumors
Mediastinoscopy: Surgical tools are inserted behind the breastbone to take tissue samples
Fine needle biopsy (FNAC): A fine needle scrapes off cells from the affected area
Biopsy: The standard gold test for cancer diagnosis

Treatment of Lung Cancer

Lung cancer treatment varies based on the stage, type, and overall health of the patient. Common approaches include surgery, radiation, chemotherapy, targeted therapy, and immunotherapy.

Surgery

Surgery is typically used for early-stage lung cancer. The procedure depends on tumor size, location, and patient health. Techniques include:

Segmental/Wedge Resection: Removes a small part of the lung.
Lobectomy: Removes an entire lobe.
Pneumonectomy: Removes an entire lung.
Sleeve Resection: Removes part of the bronchus and reconnects the lung.
Minimally invasive options like video-assisted thoracic surgery (VATS) may be used for select cases.

Radiation Therapy

Radiation uses high-energy beams to destroy cancer cells. Techniques include:

External Beam Therapy: Targets cancer precisely with minimal impact on surrounding tissue.
Proton Therapy: Delivers focused radiation with reduced exposure to healthy tissue.
Radiation may be combined with chemotherapy for enhanced effectiveness.

Chemotherapy

Chemotherapy circulates throughout the body to attack cancer cells. It may be used:

Before surgery (neoadjuvant) to shrink tumors.
After surgery (adjuvant) to eliminate remaining cancer cells.
Alone or with other treatments depending on the case.

Targeted Therapy

Targeted drugs attack specific cancer cell mechanisms. These therapies are mainly used for non-small cell lung cancer and may include medications like crizotinib, erlotinib, and cetuximab.

Immunotherapy

Immunotherapy boosts the body’s immune system to fight cancer. Drugs such as pembrolizumab, atezolizumab, and nivolumab are approved for certain lung cancers and have shown promising results. Johns Hopkins Medicine - Lung Cancer Treatment

Survival Rate

Stage 1: Almost 65 out of 100 people (almost 65%) with stage 1 lung cancer will survive their cancer for 5 years or more after they’re diagnosed.
Stage 2: Around 40 out of 100 people (around 40%) with stage 2 lung cancer will survive their cancer for 5 years or more after they’re diagnosed.
Stage 3: Around 15 out of 100 people (around 15%) with stage 3 lung cancer will survive their cancer for 5 years or more after they’re diagnosed.
Stage 4: Around 5 out of 100 people (around 5%) with stage 4 lung cancer will survive their cancer for 5 years or more after they’re diagnosed. Cancer Research UK - Lung Cancer Survival