What is lung cancer?

Lung cancer occurs when abnormal cells grow uncontrollably in the lung tissue. These abnormal cells can grow to form a tumour, and some can also spread to other parts of the body (metastasise). Whether or not a tumour metastasises determines whether or not it is benign or malignant. Benign tumours are localised and do not spread, while malignant tumours do spread. Only malignant tumours are referred to as cancerous.

The lungs are sponge-like organs located in the chest, surrounded by a protective lining called the pleura. They are divided into sections called lobes. The right lung has three lobes and the left lung has two. The left lung is smaller because the heart is also located there. When we breathe, we inhale oxygen and exhale carbon dioxide, a waste product of the body. The lungs are where this gas exchange occurs. When we breathe through our nose or mouth, air travels down the windpipe (trachea) and into the lungs via a branched airways system. This system consists of two large tubes called bronchi, which are divided into smaller branches called bronchioles. At the end of the bronchioles are small air sacs called alveoli, which is where oxygen and carbon dioxide are exchanged.

The majority of lung cancers originate in the lining of the bronchi, but they can also start anywhere in the respiratory tract, including the trachea, bronchioles and alveoli.

Anatomy of the lungs. 

Signs and symptoms

Lung cancer can present in many different ways. The most frequent symptoms are:

  • A persistent, unexplained cough or coughing up of blood;
  • Shortness of breath, and;
  • Chest pain, usually on the side where the cancer is located. 

Coughing adult.Most common symptoms of lung cancer include a persistent cough, chest pain and shortness of breath. 

Occasionally, lung cancer may be found after a chest infection, including pneumonia or frequent bouts of bronchitis. Other symptoms that may lead to lung cancer being diagnosed are unexplained weight loss or anaemia, difficulty swallowing, or enlarged lymph nodes above the collarbone.

Unfortunately, lung cancer has often spread beyond the lungs by the time it is diagnosed. Sometimes it is from metastases that symptoms can develop, including bone pain from cancer that has spread to the bones and headache or seizures from brain involvement.

Some types of lung cancer can also release substances that act on distant organs in the body. This rare occurrence is called a paraneoplastic syndrome. An example of a paraneoplastic syndrome is increased calcium levels in the blood, which causes increased thirst and urination frequency, loss of appetite, tiredness, constipation and vomiting. The calcium overproduction is due to an overstimulation of the parathyroid gland by hormones that are produced by the tumour. 

Anaemia

A deficiency in red blood cells or haemoglobin in the body.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Seizures

A sudden, involuntary contraction of muscle groups caused by abnormal electrical activity in the brain.

Causes

The cause of lung cancer, as with other cancers, is damage to cellular DNA. This damage results in uncontrolled growth of abnormal cells, which leads to formation of a tumour. The tumours can invade nearby tissue, or cancer cells can spread throughout the body via the bloodstream or lymphatic system. The cause of this cellular damage is inhalation of carcinogenic substances, such as tobacco and asbestos. Ongoing research is also discovering specific genes that result in a genetic predisposition for developing lung cancer.

DNA

The genetic material of all living cells and some viruses. The full name is deoxyribonucleic acid.

Genes

A unit of inheritance (heredity) of a living organism. A segment of genetic material, typically DNA, that specifies the structure of a protein or related molecules. Genes are passed on to offspring so that traits are inherited, making you who you are and what you look like.

Genetic predisposition

The increased likelihood of an individual to develop a medical condition based on their specific genetic profile.

Lymphatic system

A network of vessels, lymph nodes, the spleen and other organs that transport lymph fluid between tissues and bloodstream.

Risk factors

Risk factors for lung cancer include:

Smoking

Smoking, or exposure to second-hand smoke, is the single-greatest risk factor in the development of lung cancer. The risk increases the longer you smoke.

Family history

If a close blood relative has had lung cancer, you have a higher risk of developing the disease. The risk increases if they were diagnosed before the age of 50. The effect of family history may be due to shared behaviour such as smoking, but a diagnosis before 50 years of age is more likely to have a genetic component.

Ethnicity

The rates of lung cancer vary substantially between countries, possibly due to the variation in the number of people smoking. There is no clear evidence regarding ethnic variation in non-smokers.

Chemical exposure

Exposure to asbestos or other cancer-causing substances (carcinogens) such as chromium and nickel, or high levels of radon gas (found in mines), can increase the risk of developing lung cancer.

Types

Small cell lung cancer

When looking at small cell lung cancer (SCLC) under a microscope, the cells look small and the nucleus takes up most of the space inside the cells. It is also called oat cell cancer because of the oat-like appearance of the cells. This type of cancer is almost always smoking or asbestos-related.

Non-small cell lung cancer

Non-small cell lung cancer (NSCLC) covers a mixed group of lung cancers that includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma. They are named for the cells from which they originate or, as in the case of large cell carcinoma, their appearance under a microscope (large cells). Squamous cells line the bronchi, bronchiole and alveoli, while adenocarcinoma starts in the cells that produce mucus for the airways.

Differentiation of NSCLC from SCLC is important for determining treatment and predicting outcome. 

Carcinoid tumours of the lung

Carcinoid tumours are neuroendocrine tumours, which are rare cancers that originate in cells that produce hormones. They are slow-growing, often do not have any symptoms and are generally not fatal. However, a rare aggressive form of a carcinoid tumour, an adenocarcinoid tumour, has a poor prognosis.

Mucus

A thick, viscous liquid that is secreted for lubrication and to form a protective lining over certain tissues.

Adenocarcinoid tumour

A rare tumour of the gastrointestinal tract that has features of two different cancers - adenocarcinoma (gland-forming cancers) and carcinoid tumours (tumours capable of releasing hormones). These cancers can spread via lymph nodes or blood to other parts of the body.

Stages

Staging is an evaluation that doctors use to determine the most appropriate treatment plan for each patient. For lung cancer, this involves phyical characterisation of the cancer cells using a microscope, the location of the primary tumour and the extent of the cancer metastasis, to areas such as distant organs.

Stages of non-small cell lung cancer:

Stage I

The tumour is only in one lobe of the lung.

Stage II

The cancer has spread to the nearby lymph nodes or chest wall.

Stage IIIA

The cancer has spread to the lymph nodes in the centre of the chest.

Stage IIIB

The cancer has spread extensively to lymph nodes, or major blood vessels, or the trachea.

Stage IV

The cancer has spread throughout the body to other organs such as the bone.

Stages of small cell lung cancer:

Limited disease

The tumour is contained to the lung and nearby lymph nodes.

Extensive disease

The cancer has spread throughout the body.

Stages of carcinoid tumours:

As there is no recognised staging system for carcinoid tumours, they are generally described as either:

Localised

The tumour has not spread beyond its place of origin;

Regional

The cancer has spread to nearby tissues, or;

Metastasised

The cancer has spread throughout the body.

Lymph nodes

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Methods for diagnosis

When a cancer is suspected, it is usually a high priority to obtain a tissue sample for examination. This is used to determine the type of lung cancer involved, which then determines the treatment options. In lung cancer, these are the methods that may be used to obtain a tissue sample.

Sputum cytology

The mucus and phlegm (sputum) from your lungs is collected by you coughing forcefully into a sterile container and the sputum is then checked for presence of cancerous cells.

Imaging

There are several imaging tests available, including:

  • A chest X-ray, which may detect cancers that are 1 cm wide or more;
  • A computerised tomography (CT) scan, which uses X-rays to develop a 3D image of the body. This can detect smaller tumours more effectively than a simple X-ray can, and;
  • A positron emission tomography (PET) scan, which involves an injection with a radioactive substance, called a tracer, that deposits in tissues with high activity, such as cancers. CT scans can then be used to find the areas where the tracer is unusually dense, often indicating a tumour.

Procedures

Lung biopsy

When the tumour is in the outer part of the lungs, a lung biopsy can be used. This involves using an X-ray or CT scan to determine where the sample should be taken from. A medication is used to numb the skin and a fine needle used to collect the sample. The procedure carries a small risk of lung puncture.

Bronchoscopy

Bronchoscopy involves an insertion of a thin tube into your airways, via your throat and windpipe (trachea), enabling the doctor to see inside the airways. A sample of cells may be taken, either by squirting a small amount of fluid into the airways and suctioning it back out, or by using a special brush-like tool to collect the cells.

Broncoscope, Bronchoscopy.The bronchoscopy procedure. 

Endobronchial ultrasound (EBUS)

This procedure involves a doctor using an ultrasonic probe called a bronchoscope, which uses sound waves to create an image of the body, to examine the airways. It is inserted into the throat and windpipe and a biopsy of a tumour or lymph node can also be taken if necessary.

Mediastinoscopy

Mediastinoscopy is an uncommon procedure that uses a camera to examine the space between the lungs and remove some tissue if necessary. This is particularly useful for obtaining samples from lymph nodes that may have cancerous cells.

Thorascopy

Thorascopy, also an uncommon procedure, can be used to obtain images or samples from the chest cavity, if it is thought the cancer may have spread into this area.

Lymph node

A small organ of the lymphatic system containing many immune cells. Lymph nodes, also known as lymph glands, are the sites where many interactions between immune cells and foreign materials occur.

Mucus

A thick, viscous liquid that is secreted for lubrication and to form a protective lining over certain tissues.

X-ray

A scan that uses ionising radiation beams to create an image of the body’s internal structures.

Types of treatment

Surgery

There are two main surgery options for lung cancer:

  • Lobectomy - the cancerous part of the lung is surgically removed, and;
  • Pneumonectomy - a whole lung is surgically removed.

Chemotherapy

Chemotherapy works by attacking cancer cells and stopping their reproduction. Various medications are used, which can be administered intravenously or orally.

There are three general types of chemotherapy:

  • Adjuvant chemotherapy, which is given after surgery with the aim of preventing a recurrence of the cancer;
  • Neoadjuvant chemotherapy, which is given before surgery to help shrink the tumour before its removal, and;
  • Chemotherapy for advanced cancer, which uses combinations of medication, administered in cycles followed by a rest period.

Side effects occur because chemotherapy can also affect healthy cells. Your doctor will monitor your dosage carefully to ensure optimal therapeutic dosage is achieved.

Radiotherapy

In this type of therapy, focused X-rays are applied to the area where the tumour is located. When surgery is not possible, radiotherapy and chemotherapy will be the main line of treatment. As with chemotherapy, this can be used as an adjuvant and neoadjuvant therapy, or for symptom control.

Hormone therapy

This is not currently a routine treatment. Further research is needed to determine the effectiveness of hormonal therapy as a treatment for lung cancer.

Other therapies

Some people diagnosed with cancer seek out complementary and alternative therapies. None of these alternative therapies are proven to cure cancer, but some can help people feel better when used together with conventional medical treatment. It is important to discuss any treatments with your doctor before starting them.

Intravenously

Within a vein.

X-rays

A scan that uses ionising radiation beams to create an image of the body’s internal structures.

Complications

Related to treatment

Many of the treatments for lung cancer can have side effects. They include:

  • Nausea, vomiting and fatigue - chemotherapy and radiotherapy can result in nausea, vomiting and fatigue. Whether or not the treatment makes you feel sick is not an indication of how well the treatment is working;
  • Altered bowel habits - constipation and diarrhoea frequently occur during chemotherapy;
  • Joint and muscle pain - this occurs after a treatment session and can last a few days;
  • Temporary hair loss - chemotherapy results in hair loss from the head and body. It will grow back after treatment has ended, and;
  • Tingling in the hands and feet - some chemotherapeutic agents can affect the nerves. It is important to tell your doctor if you develop these symptoms.

Other complications include coughing up blood, which can be quite severe, collection of fluid within the chest cavity and recurrent chest infections.

Related to the tumour

Lung cancer can cause complications that include:

  • Bleeding - A lung cancer that is adjacent to an airway and becomes friable can result in bleeding into the airway, which can be severe. This will often result in coughing up blood;
  • Pleural effusion - this occurs when fluid builds up in the lung cavity due to the presence of cancer cells in this area. A pleural effusion can cause shortness of breath and chest pain. The fluid can be drained using a needle, and;
  • Metastases - lung cancer can spread to other organs such as the brain or bones. The growth of tumours in these locations can cause symptoms such as headaches and seizures, if there are brain metastases, or bone pain and fractures as a result of bone metastases.

Joint

A connecting surface or tissue between two bones.

Seizures

A sudden, involuntary contraction of muscle groups caused by abnormal electrical activity in the brain.

Prognosis

The prognosis of lung cancer depends on the type and stage of the cancer. On average the five-year survival rate in Australia, as of 2010, was 14%. Looking at different types of lung cancer, the five-year survival rate for small cell carcinoma is 5-8% and for non-small cell carcinoma it is between 13-16%. [1] The prognosis also varies with the type of non-small cell carcinoma, with large cell carcinoma having a poorer prognosis than adenocarcinoma and squamous cell carcinoma.

Five-year survival rates are based on people who were treated in the preceding five years. Advances in treatment since then might result in better outcomes for people with lung cancer today.

1. Cancer survival and prevalence in Australia: period estimates from 1982 to 2010. Australian Government – Australian Institute of Health and Welfare. Accessed 22 September 2014 from

External link

Prevention

Most lung cancers are caused by smoking, therefore quitting smoking is the best means of preventiing development of lung cancer. Taking precautions around hazardous materials, such as asbestos, will also reduce the risk of exposure to potential cancer triggers.

1. Cancer survival and prevalence in Australia: period estimates from 1982 to 2010. Australian Government – Australian Institute of Health and Welfare. Accessed 22 September 2014 from

External link