Lung cancer (also known as carcinoma of the lung) is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung.

If left untreated, this growth can spread beyond the lung by the process of metastasis into nearby tissue or other parts of the body. Most cancers that start in the lung, known as primary lung cancers, are carcinomas that derive from epithelial cells.

The main primary types are small-cell lung cancer (SCLC), also called oat cell cancer, and non-small-cell lung cancer (NSCLC). The most common symptoms are coughing (including coughing up blood), weight loss, shortness of breath, and chest pains.

The most common cause is long-term exposure to tobacco smoke, which causes 80–90% of lung cancers.

Nonsmokers account for 10–15% of lung cancer cases, and these cases are often attributed to a combination of genetic factors, and exposure to; radon gas, asbestos, and air pollution including second-hand smoke.

Lung cancer may be seen on chest radiographs and computed tomography (CT) scans.

The diagnosis is confirmed by biopsy which is usually performed by bronchoscopy or CT-guidance. Treatment and long-term outcomes depend on the type of cancer, the stage (degree of spread), and the person’s overall health, measured by performance status.

Common treatments include surgery, chemotherapy, and radiotherapy. NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiotherapy.

Overall, 15% of people in the United States diagnosed with lung cancer survive five years after the diagnosis, while outcomes on average are worse in the developing world. Worldwide, lung cancer is the most common cause of cancer-related death in men and women.

Signs and symptoms which may suggest lung cancer include:

Respiratory symptoms: coughing, coughing up blood, wheezing or shortness of breath

systemic symptoms: weight loss, fever, clubbing of the fingernails, or fatigue

Symptoms due to local compress: chest pain, bone pain, superior vena cava obstruction, difficulty swallowing

If the cancer grows in the airways, it may obstruct airflow, causing breathing difficulties. The obstruction can lead to an accumulation of secretions behind the blockage, and predispose to pneumonia.

Cancer develops following genetic damage to DNA and epigenetic changes. These changes affect the normal functions of the cell, including cell proliferation, programmed cell death (apoptosis) and DNA repair. As more damage accumulates, the risk of cancer increases.

Smoking, particularly of cigarettes, is by far the main contributor to lung cancer. Cigarette smoke contains over 60 known carcinogens, including radioisotopes from the radon decay sequence, nitrosamine, and benzopyrene.

Additionally, nicotine appears to depress the immune response to cancerous growths in exposed tissue.

Passive smoking—the inhalation of smoke from another’s smoking—is a cause of lung cancer in nonsmokers. A passive smoker can be classified as someone living or working with a smoker.

The lungs are commonplace for the spread of tumors from other parts of the body.

Secondary cancers are classified by the site of origin; e.g., breast cancer that has spread to the lung is called metastatic breast cancer. Metastases often have a characteristic round appearance on a chest radiograph.

Primary lung cancers themselves most commonly metastasize to the brain, bones, liver, and adrenal glands. Immunostaining of a biopsy is often helpful to determine the original source.

Lung cancer staging is an assessment of the degree of spread of cancer from its original source. It is one of the factors affecting the prognosis and potential treatment of lung cancer.

The initial evaluation of non-small-cell lung cancer (NSCLC) staging uses the TNM classification. This is based on the size of the primary tumor, lymph node involvement, and distant metastasis.

After this, using the TNM descriptors, a group is assigned, ranging from occult cancer, through stages 0, IA (one-A), IB, IIA, IIB, IIIA, IIIB and IV (four).

This stage group assists with the choice of treatment and estimation of prognosis.

Small-cell lung carcinoma (SCLC) has traditionally been classified as ‘limited stage’ (confined to one half of the chest and within the scope of a single tolerable radiotherapy field) or ‘extensive-stage’ (more widespread disease).

However, the TNM classification and grouping are useful in estimating prognosis.

For both NSCLC and SCLC, the two general types of staging evaluations are clinical staging and surgical staging.

Clinical staging is performed prior to definitive surgery. It is based on the results of imaging studies (such as CT scans and PET scans) and biopsy results.

Surgical staging is evaluated either during or after the operation and is based on the combined results of surgical and clinical findings, including the surgical sampling of thoracic lymph nodes.

Treatment for lung cancer depends on the cancer’s specific cell type, how far it has spread, and the person’s performance status.

Common treatments include palliative care, surgery, chemotherapy, and radiation therapy.

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