Lung cancer happens when certain types of lung cells mutate their DNA so that they grow out of control. The cells form a mass called a malignant tumour. Lung cancer is highly dangerous and commonly metastasizes to liver, brain and other lung tissue. Approximately 90 to 95 percent of cancers of the lung are believed to arise from the epithelial cells that line the bronchi and bronchioles of the lungs. Lung cancer can also arise from the lining of the lung and is called a mesothelioma.
Lung cancer is the most common cause of cancer deaths in the world. There are about 200,000 or more lung cancer cases diagnosed in the US and about 157,000 of these people will die from their disease. The rate of lung cancer is about 1 in 14 individuals. Most cases occur in those over the age of 65 years. Less than three percent occur in those younger than forty-five years of age. Lung cancer used to be rare until people started smoking regularly. Smoking is the number one cause of lung cancer. The incidence of lung cancer in any country is directly related to how many people smoke. In developed countries, lung cancer exceeds breast cancer in death rates among women.
As mentioned, smoking is the number one cause of lung cancer. Those with 30 pack year history of lung cancer or more are at the greatest risk. Smoking of pipes and cigars also cause lung cancer but at a lesser rate. Second-hand smoke is another cause of lung cancer as is exposure to asbestos fibres, which get stuck in the lungs and can trigger mesothelioma and other lung cancers. Smokers exposed to asbestos have an extremely high risk of lung cancer. Exposure to radon gas contributes to lung cancer. About 12 percent of lung cancer patients get it from radon exposure in the ground. There is a mild family predisposition toward getting lung cancer. Patients with chronic obstructive lung disease have a mild predisposition toward getting lung cancer at a rate that is 4-6 fold higher than other individuals. Air pollution accounts for one percent of all lung cancer cases.
Lung cancer is divided into several categories, mainly small cell cancer and non-small cell cancers. This is a classification based on the appearance of the cells under the microscope. They react differently from one another when it comes to treatment so it is important to distinguish between the two when the disease is diagnosed.
Small cell cancer makes up 20 percent of lung cancer cases. It is especially aggressive but is more sensitive to chemotherapy than non small cell carcinoma. It is strongly related to smoking history.
Non small cell carcinomas make up 80 percent of all lung cancers. There are three basic types. These include adenocarcinomas (the most common type of non small cell cancer), squamous cell cancer, which accounts for 30 percent of all non small cell carcinomas and large cell carcinomas. Some of these cancers come as mixtures of lung cancer cells. Bronchial carcinoid tumours account for 5 percent of lung cancers. They occur most commonly in young people and are unrelated to smoking. They can secrete hormones which can result in paraneoplastic syndromes. They tend to grow more slowly than other lung cancers and can be treated just with surgical resection.
Signs and symptoms of lung cancer occur in 75 percent of individuals. They include cough, production of bloody sputum, unexplained weight loss and fatigue. There can be chest pain, shoulder pain or paralysis of the vocal cords. Secondary pneumonia is common if the bronchial tree is blocked. Difficulty swallowing is another side effect. There can be many different medications related to metastasis of the lung cancer. Paraneoplastic syndromes are hormonal syndromes occurring in some lung cancers because of secretion of hormones by the cancer. Cancers can secrete cortisol and cause Cushing's syndrome.
The treatment of lung cancer includes resection of the cancer in some cases, chemotherapy and radiation therapy. Small cell cancer responds best to chemotherapy and is often not treated with surgical excision. The surgery can be the removal of the tumour, the lobe of the lung or of the entire half of the lung involved in the cancer. Radiation can be used for all types of cancer. Brachytherapy includes putting in radioactive chips or beads that direct the radiation at a specific area of the lung and doesn't employ external beam radiation.