Background
Lung cancer, or more specifically carcinoma of the lung, is a disease where epithelial (internal lining) tissue in the lung grows out of control. This leads to invasion of adjacent tissue and infiltration beyond the lungs (metastasis). Lung cancer, the most common cause of cancer-related death in men and the second most common in women, is responsible for 1.3 million deaths worldwide annually. The most common symptoms are shortness of breath, cough (including coughing up blood), and weight loss.
The main types of lung cancer are small cell lung cancer and non-small cell lung cancer. This distinction is important because non-small cell lung cancer is sometimes treated with surgery, while small cell cancer is not. Also, small cell lung cancer usually responds better to chemotherapy.
The most important cause of lung cancer is exposure to tobacco smoke.The occurrence of lung cancer in non-smokers, who account for less than 10% of cases, appears to be due to a combination of genetic factors. Radon gas, asbestos,and air pollution may also contribute to the development of lung cancer.
Lung cancer may be seen on chest x-ray and CT scan. The diagnosis is confirmed with a biopsy. This is usually performed via bronchoscopy or CT-guided biopsy.
Treatment and prognosis depend upon the histological type of cancer, the stage (degree of spread), and the patient's performance status. Possible treatments include surgery, chemotherapy, and radiotherapy. Even with treatment, the overall five-year survival rate is 14%.
ClassificationThe vast majority of lung cancers are carcinomas, namely malignancies that arise from epithelial cells. There are two main types of lung carcinoma categorized by the size and appearance of the malignant cells seen by a histopathologist under a microscope: non-small cell (80%) and small-cell (roughly 20%) lung cancer. This classification, although based on simple histological criteria, has very important implications for clinical management and prognosis of the disease.
Rarer forms of lung cancer include carcinoid, adenoid cystic carcinoma (cylindroma) and mucoepidermoid carcinoma.
Non-small cell lung cancer (NSCLC)
The non-small cell lung cancers are grouped together because their prognosis and management are similar. There are three main sub-types: squamous cell lung carcinoma, adenocarcinoma and large cell lung carcinoma. When NSCLC cannot be subtyped, it is assigned SNOMED code 8046/3.
Accounting for 29% of lung cancers, squamous cell lung carcinoma usually starts near a central bronchus. Cavitation and necrosis within the center of the cancer is a common finding. Well-differentiated squamous cell lung cancers often grow more slowly than other cancer types.
Adenocarcinoma is the most common subtype of NSCLC, accounting for 32% of lung cancers. It usually originates in peripheral lung tissue. Most cases of adenocarcinoma are associated with smoking. However, among people who have never smoked ("never-smokers"), adenocarcinoma is the most common form of lung cancer. A subtype of adenocarcinoma, the bronchioloalveolar carcinoma, is more common in female never-smokers, and may have different responses to treatment.
Accounting for 9% of lung cancers, large cell lung carcinoma is a fast-growing form that grows near the surface of the lung. It is often poorly differentiated and tends to metastasize early.
Small cell lung cancer (SCLC)
Small cell lung cancer (SCLC, also called "oat cell carcinoma") is less common. It tends to arise in the larger breathing tubes and grows rapidly, becoming quite large. The "oat" cell contains dense neurosecretory granules which give this an endocrine/paraneoplastic syndrome association. While initially more sensitive to chemotherapy, it ultimately carries a worse prognosis and is often metastatic at presentation. This type of lung cancer is strongly associated with smoking.
Metastatic cancers
The lung is a common place for metastasis from tumors in other parts of the body. These cancers are identified by the site of origin, thus a breast cancer metastasis to the lung is still known as breast cancer. They often have a characteristic round appearance on chest x-ray.
Primary lung tumors themselves most commonly metastatize to the adrenal glands, liver, brain, and bone.
Staging
- See also: Non-small cell lung cancer staging
Lung cancer staging is an assessment of the degree of spread of the cancer from its original source. It is an important factor affecting the prognosis and potential treatment of lung cancer.
Non-small cell lung cancer is staged from IA ("one A", best prognosis) to IV ("four", worst prognosis). Small cell lung cancer is classified as limited stage if it is confined to one half of the chest and within the scope of a single radiotherapy field. Otherwise it is extensive stage.
Symptoms
If the cancer grows in the airway, it may obstruct airflow, causing breathing difficulties. This can lead to accumulation of secretions behind the blockage, predisposing the patient to pneumonia.
Many lung cancers have a rich blood supply. The surface of the cancer may be fragile, leading to bleeding from the cancer into the airway. This blood may subsequently be coughed up.
Depending on the type of tumor, so-called paraneoplastic phenomena may initially attract attention to the disease. In lung cancer, these phenomena may include Lambert-Eaton myasthenic syndrome (muscle weakness due to auto-antibodies), hypercalcemia or SIADH. Tumors in the top (apex) of the lung, known as Pancoast tumors, may invade the local part of the sympathetic nervous system, leading to changed sweating patterns and eye muscle problems (a combination known as Horner's syndrome), as well as muscle weakness in the hands due to invasion of the brachial plexus.
Many of the symptoms of lung cancer (bone pain, fever, weight loss) are nonspecific; in the elderly, these may be attributed to comorbid illness. In many patients, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. Common sites of metastasis include the bone, such as the spine (causing back pain and occasionally spinal cord compression), the liver and the brain. About 10% of people with lung cancer do not have symptoms of it at the time of diagnosis; these cancers are usually found on routine chest x-rays.
Preventions
- See also: Smoking ban and List of smoking bans
Prevention is the most cost-effective means of fighting lung cancer. While in most countries industrial and domestic carcinogens have been identified and banned, tobacco smoking is still widespread. Eliminating tobacco smoking is a primary goal in the prevention of lung cancer, and smoking cessation is an important preventative tool in this process.
Policy interventions to decrease passive smoking in public areas such as restaurants and workplaces have become more common in many Western countries, with California taking a lead in banning smoking in public establishments in 1998, Ireland playing a similar role in Europe in 2004, followed by Italy and Norway in 2005, Scotland as well as several others in 2006, and England in 2007. New Zealand has also recently banned smoking in public places.
The state of Bhutan has had a complete smoking ban since 2005. In many countries, pressure groups are campaigning for similar bans. Arguments cited against such bans are criminalisation of smoking, increased risk of smuggling and the risk that such a ban cannot be enforced.
Screening
Screening refers to the use of medical tests to detect disease in asymptomatic people. Possible screening tests for lung cancer include chest x-ray or computed tomography (CT) of the chest. So far, screening programs for lung cancer have not demonstrated any clear benefit. Randomized controlled trials are underway in this area to see if decreased long-term mortality can be directly observed from CT screening.
source: Wikipedia.org
