Lung Cancer: Types, Symptoms and Treatment

Table of Contents

What is Lung Cancer?

Lung cancer is a common and serious form of cancer characterized by the uncontrolled growth of abnormal cells in the lungs.
It poses a significant health concern, leading to severe consequences and potential fatality.
Specifically, lung cancer refers to cancers originating in the lungs, typically in the bronchi, bronchioles, or alveoli—the airways and small air sacs.
Cancers originating elsewhere and spreading to the lungs are generally identified by their site of origin.

Key Facts

Lung cancer poses a significant threat to public health, resulting in a substantial number of fatalities on a global scale.
It ranks as the second most prevalent form of cancer worldwide, being the most commonly diagnosed cancer in men and the second most commonly diagnosed cancer in women.
In the year 2020 alone, there were over 2.2 million new cases of lung cancer reported.
According to the GLOBOCAN 2020 estimates by the International Agency for Research on Cancer (IARC), lung cancer remains the primary cause of cancer-related deaths, accounting for an estimated 1.8 million fatalities (18%) in 2020.
Smoking is the primary contributor to lung cancer, accounting for around 85% of total instances.
In many cases, lung cancer is identified in its later stages, leaving limited treatment possibilities.
However, by screening individuals at high risk, there exists the potential to detect the disease early, significantly enhancing chances of survival.
Implementing primary prevention measures like tobacco control and reducing exposure to environmental risk factors can effectively decrease the occurrence of lung cancer and save lives.

Types of Lung Cancer

1. Non-small cell lung cancer (NSCLC)

Non-small cell lung cancer (NSCLC) accounts for approximately 80% to 85% of all lung cancer cases.
NSCLC consists of several main subtypes, namely adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.
These subtypes originate from different types of lung cells but are categorized together as NSCLC due to their similar treatment approaches and prognoses.

i) Adenocarcinoma

Adenocarcinoma is characterized by the growth of cancerous cells that typically produce substances like mucus.
While it is commonly associated with individuals who smoke or have a history of smoking, it is also prevalent in nonsmokers.
Additionally, adenocarcinoma is more frequently diagnosed in women and younger individuals compared to other types of lung cancer.
It tends to develop in the outer regions of the lung and is often detected at an early stage before it spreads.

ii) Squamous cell carcinoma

Squamous cell carcinoma starts in squamous cells, which are flat cells lining the airways within the lungs.
It is commonly linked to a history of smoking and tends to be found in the central part of the lungs near the primary airway (bronchus).
Large cell (undifferentiated) carcinoma
Large cell carcinoma can develop in any area of the lung.
It has a tendency to grow and metastasize rapidly, posing challenges for effective treatment.
A specific subtype of large cell carcinoma called large cell neuroendocrine carcinoma (LCNEC) exhibits aggressive growth and bears resemblance to small cell lung cancer.

iii) Other subtypes

There exist a few other less prevalent subtypes of NSCLC, such as adenosquamous carcinoma and sarcomatoid carcinoma.

iv) Small cell lung cancer (SCLC)

SCLC, also known as oat cell cancer, accounts for approximately 10% to 15% of lung cancer cases.
It has a tendency to exhibit rapid growth and metastasis compared to NSCLC.
Typically, SCLC is already in an advanced stage when diagnosed, having spread beyond the lungs.
Due to its aggressive nature, chemotherapy and radiation therapy are often effective treatment options.
Unfortunately, the majority of individuals with SCLC will experience a recurrence of the cancer at some stage.

Causes of Lung Cancer

Lung cancer can affect anyone, regardless of their background.
It occurs due to genetic alterations or mutations in lung cells.
There are multiple factors that can trigger these mutations, resulting in a permanent change in the DNA sequence of a gene.
Typically, the transformation of lung cells is associated with the inhalation of hazardous and harmful substances.
It’s important to note that even if an individual had been exposed to these substances many years ago, the risk of developing lung cancer remains present.

Risk Factors

1. Modifiable Risk Factors:

Smoking

Cigarette smoking is the leading cause of lung cancer.
The risk increases with the number of cigarettes smoked and the duration of smoking. Quitting smoking can significantly reduce the risk.

Secondhand Smoke

Being exposed to smoke from others who are smoking increases the risk of developing lung cancer.

Occupational Exposure

Exposure to harmful substances like asbestos, radon, arsenic, uranium, and certain industrial chemicals can increase the risk.

Air Pollution

Prolonged exposure to air pollution, such as from vehicle emissions or industrial pollutants, may contribute to an increased risk of lung cancer.

2. Non-Modifiable Risk Factors:

Family History

Having a first-degree relative (parent, sibling, or child) with lung cancer increases the risk.

Genetic Predisposition

Certain genetic mutations, such as alterations in the EGFR or ALK genes, can increase susceptibility to lung cancer.

Previous Radiation Therapy

Individuals who have received radiation therapy to the chest for a different cancer may have an elevated risk of developing lung cancer.

Pre-existing Lung Diseases

Chronic lung diseases like chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis can raise the risk of lung cancer.

High Risk Groups

Current smokers or individuals with a history of smoking have the highest risk of developing lung cancer.
People regularly exposed to secondhand smoke, especially in enclosed spaces or for prolonged periods, are at an increased risk.
Certain occupations, such as construction workers, miners, and industrial workers, are exposed to carcinogens and have a higher risk.
Those with a family history of lung cancer, particularly in first-degree relatives, are at an increased risk.
Individuals who have undergone radiation therapy to the chest for a different type of cancer have an elevated risk of developing lung cancer.

Signs and Symptoms of Lung Cancer

A persistent cough that lingers.
Experiencing chest pain.
Feeling a difficulty in breathing.
Coughing up blood (haemoptysis).
Fatigue
Undergoing unexplained weight loss.
Suffering from recurrent lung infections.

Stages of Lung Cancer

Stage 0 (in-situ):

The top lining of the lung or bronchus contains cancer, but it has not spread to other parts of the lung or beyond.

Stage I:

Cancer remains confined within the lung and have not spread beyond it.

Stage II:

The cancer has grown larger compared to Stage I and has extended to lymph nodes within the lung, or there are multiple tumors present in the same lobe of the lung.

Stage III:

The cancer has surpassed Stage II in size and has spread to neighboring lymph nodes or structures, or there are multiple tumors located in a different lobe of the same lung.

Stage IV:

Cancer has spread to the other lung, the fluid surrounding the lung, the fluid surrounding the heart, or distant organs.

Screening

People at high risk of developing lung cancer should consider undergoing regular screening.
A low dose CT scan is used for screening.
According to the American Lung Association (ALA), individuals who meet the following criteria are recommended to undergo screening:
They fall within the age range of 55-80 years.
They have a history of heavy smoking, defined as 30 pack years, which equates to smoking one pack per day for 30 years or two packs per day for 15 years.
They either currently smoke or have quit smoking within the past 15 years.

Diagnosis of Lung Cancer

Doctors perform a physical examination to detect lung cancer and employ imaging techniques like chest X-rays, computed tomography scans, and magnetic resonance imaging for diagnosis.
They also examine the inside of the lung by performing a bronchoscopy. To determine the specific subtype of lung cancer (NSCLC versus SCLC), they take a tissue sample (biopsy) for histopathology examination.
Additionally, they conduct molecular testing to identify particular genetic mutations or biomarkers that help determine the most suitable treatment option.

Prevention of Lung Cancer

The most important step in preventing lung cancer is to avoid smoking and exposure to secondhand smoke.
Quitting smoking significantly reduces the risk of developing lung cancer.
Radon is a radioactive gas that can accumulate in homes and buildings.
Testing for radon and taking measures to reduce its levels can help prevent lung cancer.
Following safety guidelines and using protective equipment in occupation where there is exposure to certain chemicals and substances can reduce exposure.
Ensuring good indoor and outdoor air quality can help prevent lung cancer.
Avoiding exposure to air pollution and using proper ventilation systems are important measures.
Consuming a balanced diet rich in fruits, vegetables, and whole grains, while limiting processed foods, can contribute to overall health and reduce the risk of lung cancer.
Engaging in regular physical activity can help maintain a healthy weight and reduce the risk of various types of cancer, including lung cancer.
For individuals at high risk, such as current or former smokers, regular screening with low-dose computed tomography (LDCT) can help detect lung cancer at an early stage when it is more treatable.

Treatment of Lung Cancer

Surgery
Radiotherapy (radiation)
Chemotherapy
Targeted therapy
Immunotherapy

Fatality rate or survival rate

The non-small-cell lung cancer (NSCLC) shows the following relative survival rates:

When the cancer is localized, confined to one lung, the survival rate is 60%.
If the cancer has spread outside the lung or to lymph nodes, categorized as regional, the survival rate is 33%.
When the cancer has moved farther, reaching the brain, the other lung, and bones, classified as distant, the survival rate drops to 6%.
Overall, across all stages of NSCLC, the relative survival rate is 23%.

As for the small-cell lung cancer (SCLC), which is a rare but aggressive form of lung cancer, the relative survival rates are as follows:

In cases where the cancer is localized, the survival rate is 29%.
If the cancer has progressed regionally, the survival rate decreases to 15%.
When the cancer has spread to distant parts like the brain, the other lung, and bones, the survival rate further reduces to 3%.
Across all stages of SCLC, the relative survival rate is 6%.