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The body’s cells have self-control mechanisms that ensure the organs grow in a well structured manner. When these cells experience uncontrolled growth they form tumours. When these cells not only grow but also invade other tissues or organs through the blood stream (metastasis), then this is defined as cancer.
The majority of lung cancers begin with disorderly growth of the cells covering the bronchi in the lungs.
The lungs are located in the chest cavity and are responsible for oxygenating our blood when we breathe. Air reaches the lungs via the trachea and bronchi.
The lungs are composed of thousands of tiny sacs, called alveoli, which supply oxygen and eliminate carbon dioxide from the blood (gas exchange). When inhaling air we absorb oxygen and when exhaling we eliminate carbon dioxide.
The lungs are surrounded by a thin double membrane called the pleura. One membrane covers the chest cavity and the other the lung. There is a small volume of liquid between the two membranes. The two membranes are attached to each other but they can also move around.
This particularity means the lungs can remain attached to the chest wall whist simultaneously expanding and contracting in synchronisation with each breathe. The two pleural membranes are joined together in the same way as two sheets of glass separated by a thin layer of water; they can move over each other but it requires a lot of force to separate them.
How many people does it affect?
Lung cancer has the highest global mortality rate of all tumours. The Spanish Society of Medical Oncology (SEOM), in their 2012 annual report, indicates that in Spain lung cancer is the second most common cancer in men and the fourth in women. However, lung cancer causes the highest number of deaths due to cancer.
The incidence in Spain is expected to increase over the next 20 years, not only in men but also in women, due to an increased number of people smoking. On average, lung cancer is diagnosed at the age of 65.
Types of lung cancer
Lung cancer is divided into two major types depending on the shape of the cells causing the disease. Classification of tumour type is an essential step before selecting treatment.
1. Small cell lungcancer (or microcytic cancer). Represents around 15–20% of all lung cancers. It is characterised by its aggressive nature, rapid growth, and its tendency to affect the central ganglia and to spread to the brain.
2. Non-small cell lung cancer. This is the most common type of lung cancer (80%).
It is further categorised into three subtypes:
Adenocarcinoma. The most common subtype of lung cancer. It usually affects the more peripheral areas of the lung and of all subtypes it has the greatest tendency to spread to other organs (metastasis). Adenocarcinoma is characteristically seen in smokers; nevertheless, the rate of incidence in non-smokers is currently on the increase.
Squamous cell carcinoma (or epidermoid carcinoma). The most frequently occurring subtype of lung cancer, along with adenocarcinoma. It tends to grow in a central location and occurs exclusively in smokers.
Large cell carcinoma. Is a less common subtype characterised by the large size of the cells involved. It tends to be the most aggressive of all lung cancers.