Lung cancer

What is cancer of the lung?
Cancer of the lung, like all cancers, results from an abnormality in the body's basic unit of life, the cell. Normally, the body maintains a system of checks and balances on cell growth so that cells divide to produce new cells only when needed. Disruption of this system of checks and balances on cell growth results in an uncontrolled division and proliferation of cells that eventually forms a mass known as a tumor.
Tumors can be benign or malignant; when we speak of "cancer," we refer to those tumors that are considered malignant. Benign tumors can usually be removed and do not spread to other parts of the body. Malignant tumors, on the other hand, grow aggressively and invade other tissues of the body, allowing entry of tumor cells into the bloodstream or lymphatic system and then to other sites in the body. This process of spread is termed metastasis; the areas of tumor growth at these distant sites are called metastases. Since lung cancer tends to spread or metastasize very early in its course, it is a very life-threatening cancer and one of the most difficult cancers to treat. While lung cancer can spread to any organ in the body, certain organs -- particularly the adrenal glands, liver, brain, and bone -- are the most common sites for lung-cancer metastasis.
The lung is also a very common site for metastasis from tumors in other parts of the body.

The principal function of the lungs is the exchange of gases between the air we breathe and the blood. Through the lung, carbon dioxide is removed from the bloodstream and oxygen from inspired air enters the bloodstream. The right lung has three lobes, while the left lung is divided into two lobes and a small structure called the lingula that is the equivalent of the middle lobe. The major airways entering the lungs are the bronchi, which arise from the trachea. The bronchi branch into progressively smaller airways called bronchioles that end in tiny sacs known as alveoli where gas exchange occurs. The lungs and chest wall are covered with a thin layer of tissue called the pleura.
Lung cancers can arise in any part of the lung, but 90%-95% of cancers of the lung are thought to arise from the epithelial, or lining cells of the larger and smaller airways (bronchi and bronchioles); for this reason, lung cancers are sometimes called bronchogenic carcinomas or bronchogenic cancers. Cancers can also arise from the pleura (the thin layer of tissue that surrounds the lungs), called mesotheliomas, or rarely from supporting tissues within the lungs, for example, blood vessels.

General symptoms of lung cancer

* Having a cough most of the time
* A change in a cough you have had for a long time
* Being short of breath
* Coughing up phlegm (sputum) with signs of blood in it
* An ache or pain when breathing or coughing
* Loss of appetite
* Fatigue
*Losing weight

Less common symptoms of lung cancer

There are other symptoms of lung cancer that are less common. They are usually associated with more advanced lung cancer. You may have
* A hoarse voice
* Difficulty swallowing
* Swelling of the face caused by a blockage of a main blood vessel from the head (SVCO)
* Swelling in the neck caused by enlarged lymph nodes
* Pain or discomfort under your ribs on your right side (from the liver)
* Shortness of breath caused by fluid around the lungs (called pleural effusion)
* Swollen face caused by superior vena cava obstruction (SVCO)The vena cava is a large vein that carries blood from the brain and head back to the heart. If it is blocked, there is a build up behind the blockage causing fluid to seep out from the bloodstream and collect in the tissues of the face, causing swelling. This is called superior vena cava obstruction or SVCO for short.All of these symptoms can be caused by other diseases apart from lung cancer. So, you should always see your doctor if you are worried about any symptoms. You may have a chest infection, or other illness that is easily treatable. If you do have lung cancer, the earlier it is diagnosed, the easier it is to treat it.

Causes
Lung cancer most commonly begins in the cells that line your lungs. Smoking causes the majority of lung cancers — both in smokers and in people exposed to secondhand smoke. But lung cancer also occurs in people who never smoked. In these cases, there may be no clear cause of lung cancer. Doctors have identified factors that may increase the risk.
How smoking causes lung cancer Doctors believe smoking causes lung cancer by damaging the cells that line the lungs. When you inhale cigarette smoke, which is full of cancer-causing substances (carcinogens), changes in the lung tissue begin almost immediately. At first your body may be able to repair this damage. But with each repeated exposure, normal cells that line your lungs are increasingly damaged. Over time, the damage causes cells to act abnormally and eventually cancer may develop.
Your lungs are full of blood vessels and lymph vessels, giving lung cancer cells easy access to travel to other parts of your body. For this reason, lung cancer may spread to other parts of your body before you experience any signs or symptoms. In many cases, lung cancer may spread before it can even be detected in the lungs.