Lung cancer is caused by uncontrolled rapid growth of cells in tissues. This type of cancer is most common and results in more than a million deaths every year. This form of cancer is indicated by weight loss or coughing up blood or regularly going out of breath. It can be noticed on chest radio graph also called CT Scan. The treatment that one gets depends on the stage that one is in. Treatment of cancer include surgery, chemotherapy and radiotherapy.CLASSIFICATIONLung cancers are classified after studying under them microscope. Classification is necessary as different type of cancer is treated differently. Large portion of lung cancer are carcinomas – malignancies that grow from epithelial cells. Lung-carcinomas are categorized into two types: non -small and small-cell lung carcinoma. Non-small cell lung carcinoma and small cell lung carcinoma account for 80. 4% and 16. 8% frequency of lung cancer, respectively.1. NON -SMALL CELL LUNG CARCINOMA The non -small cell lung carcinomas are grouped together as their prognosis and management are same up to some extent. They are further classified into three types: squamous cell lung carcinoma, adenocarcinoma and large cell lung carcinoma. Squamous cell lung cancer originates near a central bronchus. They account for 25% of lung cancers. Adenocarcinoma starts in peripheral lung tissue. The cases of adenocarcinoma are a result of smoking. They accounts to 40% of non -small cell lung cancers.2. SMALL CELL LUNG CARCINOMA This type of lung cancer is rare. It is sometimes referred to as “oat cell” carcinoma. Most of the times they originate from larger airways (primary and secondary bronchi ) and from there they grow at a rapid pace. This type of lung cancer if mostly associated with smoking.SECONDARY CANCERS These cancers are classified on the basis of site of origin like breast cancer but has spread to the lung. Majority of the lung cancers in children are secondary.STAGING OF LUNG CANCERLung cancer staging is used to asses the degree of spread of the cancer from its place of origin. It is an important factor that determines the potential treatment of lung cancer. The degree starts from 1A to 4, 1A being best prognosis and 4 being worst.SIGNS AND SYMPTOMS Following are the symptoms of lung cancer: 1. Voice becoming hoarse. 2. Sudden loss of weight. 3. Feeling pain in chest region or abdomen. 4. Difficulty in swallowing. 5. Loss of appetite. 6. Running out of breath. Many of the symptoms mentioned above are non -specific. By the time they notice symptoms or signs, cancer has already spread from place of origin. Very few people with this cancer have signs at time of diagnosis, these cancers are noticed on routine chest radio graph.CAUSES The three main causes of cancer are: carcinogens (which is found in tobacco ), viral infection and ionizing radiation. If exposed, it causes changes to DNA in tissue lining the bronchi of the lungs. With more and more tissues getting damaged, cancer develops.1. SMOKING Smoking is the main cause of cancer. In one cigarette, there are 60 different known types of carcinogens like radioisotopes and nitrosamine. Smoking is believed to cause 80% of these type of cases. The risk is generally less in non -smokers. The time that a person smokes proportionately increases the chances of this cancer. There has been cases that if a person stops smoking, the damaged cells gradually gets repaired. In non-smokers, passive smoking is the main causes of lung-cancer. Passive smoking is one inhaled from another person smoking.2. RADON GASThe gas produced from breakdown of radium. This gas is colourless and odorless. Exposure to radiation ionize the genetic material, causing mutations that sometimes turn cancerous. Exposure to radon gas is the second major cause of lung-cancer after smoking.3. ASBESTOS Asbestos is responsible for causing a number of cancer, one among them is lung cancer. In UK, asbestos accounts for 2 to 3% of the total cases of this cancer.4. VIRUS Viruses are responsible for causing lung-cancer in animals. And research has shown of similar potential in humans.5. PARTICULATE MATTERParticulate matter has a direct link to lung cancer cases. The size and quantity of particles in air determines the risk of getting lung-cancer. If concentration of particles increases beyond 1%, then the chances of getting this increases by 14%.PATHOGENESISJust like may other cancer forms, lung cancer is started by activation of ocnogenes or inactivation of tumor suppressing genes. Ocnogenes are those genes that make people more vulnerable to cancer. Ocnogenes are produced from proto-ocnogenes, when the latter is exposed to particular carcinogens. In k-ras proto-oncogene, mutations takes place which are responsible for 10 to 30% of lung adenocarcinomas. Tumor invasion, angiogenesis, apoptosis, cell profileration are regulated by the Epidermal growth factor receptor. Mutations and amplification of EGFR are common in non -small cell lung cancer. The basis for treatment with EGFR-inhibitors are also provided by Mutation and amplification of EGFR. Chromosomal damage can lead to loss of heterozygosity which can result in inactivation of tumor suppressor genes. Damage to four of these chromosomes:3p, 5q, 13 q and 17 p are common in small cell lung-carcinoma. The p53, which is a tumor suppressor gene, located on chromosome 17p is affected in most of the cases. c-MET, NKX2-1, LKB1, PIK3A and BRAF are also mutated or amplified. Various genetic polymorphisms are supplementary to this cancer. Some of them include polymorphisms in genes coding for interleukin-1, cytochrome p450, apoptosis promoters such as caspase-8, and XRCC1, which is DNA repair molecule. People having these polymorphisms are more likely to develop lung cancer on being exposed to carcinogens. The research has revealed that MDM2 309G allele is a low-penetrant risk factor for developing this in Asians.DIAGNOSIS If a person has reported symptoms that might suggest cancer related to lungs, then chest radio graph is performed in the first step. The test reveals the widening of mediastinium, atelectasis and pleural effusion. Even if there are no radio graphic findings but the hint of this is high because of things like the person being heavy smoker with blood-stained sputum then CT-Scan may provide the necessary data. If findings are unnatural in cells in sputum, then they multiplies the risk of this type of cancer. Early detection can be done by Sputum cytologic examination together with other screening examinations. The differential diagnosis for those patients who show irregularities on chest cardiograph consider cancer related to lungs along with non malignant diseases. These consider infectious reasons like tuberculosis or pneumonia. The above mentioned diseases can lead to lung nodules.PREVENTION Prevention, just like always, is better than cure. Steps in this direction have been taken by may countries by identifying carcinogens and banning them but tobacco, which is the major cause of lung cancer, is still common. Eliminating cigarette smoking is first hand target in the prevention of lung cancer. Steps to lessen Passive smoking have also being taken by banning smoking in public places and workplaces. New Zealand has restricted smoking in open places. A similar step is also taken by Chandigarh, India. Bhutan has criminalized smoking since 2005.SCREENING Screening is used to detect disease by doing medical tests when the patient is not showing any symptoms. Chest radio graph or computed tomography are the tests used for screening of lung cancer. But, results have shown, that screening tests for lung cancer rarely has shown any benefit.TREATMENTThe treatment of lung cancer can be done in following ways, depending on the stage or degree of cancer:1. SURGERYIf doctors have detected lung cancer, then CT scan and positron emission tomography are usually applied to check if the disease is placed and surgery can be done or it has moved to the point where performing surgery is not possible. Surgery can only be performed if spirometry reveals good respiratory reserve, but if it is poor, then surgery is not possible. Even surgery has a death operative rate of 4. 4% but that is because of patient’s lung function and other factors.2. CHEMOTHERAPY Chemotherapy, along with radiation, is used to treat small cell lung carcinoma. Primary chemotherapy is also used in metastatic non -small cell lung carcinoma.3. RADIOTHERAPYRadiotherapy, with chemotherapy, is given when patient is not fit to under go surgery. This type of high intensity radiotherapy is called radical radiotherapy. CHART (continuos hyperfractioned accelerated radiotherapy ) is refined version of this technique in which a high dose of radiotherapy is given for a short period of time. When cancer affects a short section of bronchus, then brachytherapy is given.EPIDEMOLOGY Lung cancer is the most widely reported cancer. There are 1. 35 million cases every year and 1. 18 million deaths. Lung cancer develop among those who have a history of smoking over a long period of years i. e 50 years and above. In addition to smoking, passive smoking is also a factor that causes lung cancer. Even the emissions from factories, automobiles, power plants pose a threat to human health. Lung cancer is found to have a reciprocal effect with sunlight and UVB exposure. This is due to effect of Vitamin D, produced in skin during exposure to sunlight.