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 new cells are 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

Lung Cancer Symptoms and Signs

In up to 25% of people who get lung cancer, there are no apparent symptoms at the time of diagnosis. In others, symptoms can occur from the cancer itself, from the metastatic spread of the cancer beyond its origin in the lung, or from so-called paraneoplastic syndromes that result from the production of hormone-like substances by the lung cancer cells. Common symptoms include:

  • Cough
  • Shortness of breath
  • Wheezing
  • Chest pain, and
  • Coughing up blood.

Other symptoms can include shoulder pain, hoarseness, or difficulty swallowing. Symptoms of metastatic disease can include headaches, vision changes, seizures, weakness, or symptoms of stroke. Symptoms common to many cancers include fatigue, unexpected weight loss, and depression.

What causes Lung Cancer ?

Lung cancer was not common prior to the 1930s but increased dramatically over the following decades astobacco smoking increased. In many developing countries, the incidence of lung cancer is beginning to fall following public education about the dangers of cigarette smoking and the introduction of effective smoking-cessation programs. Nevertheless, lung cancer remains among the most common types of cancers in both men and women worldwide.

Smoking

The incidence of lung cancer is strongly correlated with cigarette smoking, with about 90% of lung cancers arising as a result of tobacco use. The risk of lung cancer increases with the number of cigarettes smoked and the time over which smoking has occurred.

Tobacco smoke contains over 4,000 chemical compounds, many of which have been shown to be cancer-causing or carcinogenic. The two primary carcinogens in tobacco smoke are chemicals known as nitrosamines and polycyclic aromatic hydrocarbons.

Passive smoking

Passive smoking or the inhalation of tobacco smoke by nonsmokers who share living or working quarters with smokers, also is an established risk factor for the development of lung cancer. Research has shown that nonsmokers who reside with a smoker have a 24% increase in risk for developing lung cancer when compared with nonsmokers who do not reside with a smoker. The risk appears to increase with the degree of exposure (number of years exposed and number of cigarettes smoked by the household partner).

Asbestos fibers

Asbestos fibers are silicate fibers that can persist for a lifetime in lung tissue following exposure to asbestos. The workplace was a common source of exposure to asbestos fibers, as asbestos was widely used in the past as both thermal and acoustic insulation. Today, asbestos use is limited or banned in many countries.

Types of Lung Cancer?

Lung cancers, also known as bronchogenic carcinomas, are broadly classified into two types: small cell lung cancers (SCLC) and non-small cell lung cancers (NSCLC). This classification is based upon the microscopic appearance of the tumor cells themselves.

SCLC comprise about 20% of lung cancers and are the most aggressive and rapidly growing of all lung cancers. SCLC are strongly related to cigarette smoking, with only 1% of these tumors occurring in nonsmokers. SCLC metastasize rapidly to many sites within the body and are most often discovered after they have spread extensively. Referring to a specific cell appearance often seen when examining samples of SCLC under the microscope, these cancers are sometimes called oat cell carcinomas.

NSCLC are the most common lung cancers, accounting for about 80% of all lung cancers. NSCLC can be divided into three main types that are named based upon the type of cells found in the tumor:

Adenocarcinomas are the most commonly seen type of NSCLC in the U.S. and comprise up to 50% of NSCLC. While adenocarcinomas are associated with smoking, like other lung cancers, this type is observed as well in nonsmokers who outer, or peripheral, areas of the lungs.

Bronchioloalveolar carcinoma is a subtype of adenocarcinoma that frequently develops at multiple sites in the lungs and spreads along the preexisting alveolar walls.

Squamous cell carcinomas were formerly more common than adenocarcinomas; at present, they account for about 30% of NSCLC. Also known as epidermoid carcinomas, squamous cell cancers arise most frequently in the central chest area in the bronchi. Large cell carcinomas, sometimes referred to as undifferentiated carcinomas, are the least common type of NSCLC.

Mixtures of different types of NSCLC are also seen.

Other types of cancers can arise in the lung; these types are much less common than NSCLC and SCLC and together comprise only 5%-10% of lung cancers:

Bronchial carcinoids account for up to 5% of lung cancers. These tumors are generally small (3 cm-4 cm or less) when diagnosed and occur most commonly in people under 40 years of age. Unrelated to cigarette smoking, carcinoid tumors can metastasize, and a small proportion of these tumors secrete hormone-like substances that may cause specific symptoms related to the hormone being produced. Carcinoids generally grow and spread more slowly than bronchogenic cancers, and many are detected early enough to be amenable to surgical resection.

Cancers of supporting lung tissue such as smooth muscle, blood vessels, or cells involved in the immune response can rarely occur in the lung.

When should one consult a doctor?

One should consult a health-care professional if he or she develops the symptoms associated with lung cancer, in particular, if they have

  •  A new persistent cough or worsening of an existing chronic cough,
  • Blood in the sputum,
  • Persistent bronchitis or repeated respiratory infections,
  • Chest pain,
  • Unexplained weight loss and/or fatigue,
  • Breathing difficulties such as shortness of breath or wheezing.

How is Lung Cancer Diagnosed?

History and Physical examination

Chest X-ray

CT (computerized tomography, computerized axial tomography, or CAT) scans may be performed on the chest, abdomen, and/or brain to examine for both metastatic and lung tumors.

Magnetic resonance imaging (MRI) scans may be appropriate when precise detail about a tumor’s location is required.

Positron emission tomography (PET) scanning is a specialized imaging technique that uses short-lived radioactive drugs to produce three-dimensional coloured images of those substances in the tissues within the body.

Bone scans are used to create images of bones on a computer screen or on film. Doctors may order a bone scan to determine whether a lung cancer has metastasized to the bones.

Sputum cytology: The diagnosis of lung cancer always requires confirmation of malignant cells by a pathologist, even when symptoms and X-ray studies are suspicious for lung cancer. The simplest method to establish the diagnosis is the examination of sputum under a microscope.

-Bronchoscopy: Examination of the airways by bronchoscopy (visualizing the airways through a thin, fiberoptic probe inserted through the nose or mouth) may reveal areas of tumor that can be sampled (biopsied) for diagnosis by a pathologist.
Needle biopsy: Fine-needle aspiration (FNA) through the skin, most commonly performed with radiological imaging for guidance, may be useful in retrieving cells for diagnosis from tumor nodules in the lungs

-Thoracentesis: Sometimes lung cancers involve the lining tissue of the lungs (pleura) and lead to an accumulation of fluid in the space between the lungs and chest wall (called a pleural effusion). Aspiration of a sample of this fluid with a thin needle (thoracentesis) may reveal the cancer cells and establish the diagnosis.

-Molecular testing: For advanced NSCLCs, molecular genetic testing is carried out to look for genetic mutations in the tumor. For example, testing may be done to look for mutations or abnormalities in the epithelial growth factor receptor (EGFR) and the anaplastic lymphoma kinase (ALK) genes. Other genes that may be mutated include MAPK and PIK3. Targeted therapies are available that may be administered to patients whose tumors have alterations in these genes.

What is the treatment of lung cancer?

Treatment for lung cancer can involve surgical removal of the cancer, chemotherapy, or radiation therapy, as well as combinations of these treatments. The decision about which treatments will be appropriate for a given individual must take into account the location and extent of the tumor as well as the overall health status of the patient.

Surgery: Surgical removal of the tumor is generally performed for limited-stage (stage I or sometimes stage II) NSCLC and is the treatment of choice for cancer that has not spread beyond the lung.

Radiation: Radiation therapy may be employed as a treatment for both NSCLC and SCLC. Radiation therapy uses high-energy X-rays or other types of radiation to kill dividing cancer cells. Radiation therapy may be given as curative therapy, palliative therapy (using lower doses of radiation than with curative therapy), or as adjuvant therapy in combination with surgery or chemotherapy.

Radiation therapy does not carry the risks of major surgery, but it can have unpleasant side effects, including fatigue and lack of energy.

Chemotherapy: Both NSCLC and SCLC may be treated with chemotherapy. Chemotherapy refers to the administration of drugs that stop the growth of cancer cells by killing them or preventing them from dividing. Chemotherapy may be given alone, as an adjuvant to surgical therapy, or in combination with radiotherapy. While a number of chemotherapeutic drugs have been developed, the class of drugs known as the platinum-based drugs have been the most effective in treatment of lung cancers.
Chemotherapy may be given as pills, as an intravenous infusion, or as a combination of the two. Chemotherapy treatments usually are given in an outpatient setting. A combination of drugs is given in a series of treatments, called cycles, over a period of weeks to months, with breaks in between cycles. Unfortunately, the drugs used in chemotherapy also kill normally dividing cells in the body, resulting in unpleasant side effects. Damage to blood cells can result in increased susceptibility to infections and difficulties with blood clotting (bleeding or bruising easily). Other side effects include fatigue, weight loss, hair loss, nausea, vomiting, diarrhea, and mouth sores. The side effects of chemotherapy vary according to the dosage and combination of drugs used and may also vary from individual to individual. Medications have been developed that can treat or prevent many of the side effects of chemotherapy. The side effects generally disappear during the recovery phase of the treatment or after its completion.

Targeted Therapy: Molecularly targeted therapy involves the administration of drugs that have been identified to work in subsets of patients whose tumors have specific genetic changes

How can lung cancer be prevented?

Cessation of smoking and eliminating exposure to tobacco smoke is the most important measure that can prevent lung cancer. Many products, such as nicotine gum, nicotine sprays, or nicotine inhalers, may be helpful to people trying to quit smoking. Minimizing exposure to passive smoking also is an effective preventive measure. Using a home radon test kit can identify and allow correction of increased radon levels in the home. Methods that allow early detection of cancers, such as the helical low-dose CT scan, also may be of value in the identification of small cancers that can be cured by surgical resection and prevented from becoming widespread, incurable, metastatic cancer.