Lung cancer

Lung cancer is a malignant tumour of the lungs. Most commonly it is bronchogenic carcinoma (about 90%). Lung cancer is the most lethal malignant tumour worldwide, causing up to 3 million deaths.

The incidence of lung cancer is highly correlated with smoking.

Exposure to carcinogens, such as those present in tobacco smoke, immediately causes small changes to the tissue lining the bronchi of the lungs (the bronchial mucous membrane). This effect is cumulative, and over time with continued exposure more and more tissue gets damaged until a tumour develops. If the tumour grows inwards it may obstruct the air passageway, causing breathing difficulties. The lungs may then collapse and infections can develop, leading to lung abscess. The patient here would start to cough up blood-stained material. However, if the tumour grows outwards in to the lung it may not even be noticed by the patient before it starts to spread to other parts of the body.

1 Signs and symptoms
2 Types
3 Causes
4 Treatment
5 Epidemiology
6 Prevention
7 See also
8 External links

Signs and symptoms

Common symptoms include:

coughing up blood
a bad, chronic cough
wheezing
chest pains
weight loss or loss of appetite
shortness of breath
a hoarse voice
fatigue

Depending on the type of tumor, so-called paraneoplastic phenomena may initially attract attention to the disease. In lung cancer, this may be Lambert-Eaton myasthenic syndrome (muscle weakness due to auto-antibodies), hypercalcemia and 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.

Types

There are two main types of lung cancer categorised by the size and appearance of the malignant cells seen by a histopathologist under a microscope: small and non-small cell lung cancer. This classification although based on simple pathomorphological criteria has very important implications for clinical management and prognosis of the disease.

Small cell lung cancer

Small cell carcinoma (also called oat cell carcinoma) is the less common form of lung cancer, making up 20% of cases. It tends to start in the larger breathing tubes and grows rapidly becoming quite large.

Non-small cell lung cancer

Epidermoid carcinoma (or Squamous cell carcinoma) also starts in the larger breathing tubes but grows slower meaning that the size of these tumours varies when on diagnosis.

Adenocarcinoma (or for slower growing forms alveolar cell cancer) is a form which starts near the gas-exchanging surface of the lung.

Large cell carcinoma is a fast-growing form that grows near the surface of the lung.

Other types

The listed types add up to 90% of all cases of lung cancer. Other forms include carcinoid, cylindroma, mucoepidermoid and malignant mesothelioma.

Causes

Cancer death rates in the United States.

There are four major causes of lung cancer (and, actually, cancer in general):

Carcinogens such as those in cigarette smoke
Radiation exposure
Genetic susceptibility
Viral infection

Smoking, particularly of cigarettes, is believed to be by far the main cause of lung cancer, which at least in theory makes it one of the easiest diseases to prevent. An estimated 80% of lung cancers result from smoking due to the hundreds of known carcinogens—such as polynuclear aromatic hydrocarbons—present in cigarette smoke. The length of time a person continues to smoke as well as the amount smoked increases the person's chances of contracting lung cancer. If a person stops smoking, these chances steadily decrease as the lung damage is repaired.

Passive smoking—the inhalation of smoke from another's smoking—has recently been identified as a much larger cause of lung cancer in non-smokers than previously believed. The US Environmental Protection Agency (EPA) in 1993 concluded that about 3,000 lung cancer-related deaths a year were caused by passive smoking, though the true extent is still contested by scientists.

Asbestos is another carcinogen, widely known for causing mainly mesothelioma (cancer affecting the mesothelium lining the lungs, abdomenal cavity, and heart). Often this exposure happens unintentionally, for instance as a consequence of work. Smoking has been shown to considerably increase the risk that asbestos exposure will cause cancer.

Radon is a colorless and odorless gas generated by the breakdown of radioactive radium, which in turn is the decayed product of uranium, found in the earth's crust. Radon exposure is the second major cause of lung cancer after smoking. The radiation ionises genetic material, causing mutations that sometimes turn cancerous. Radon gas levels vary by locality and the composition of the underlying soil and rocks. For example, in areas such as Cornwall in the UK (which has granite as substrata), radon gas is a major problem, and buildings have to be force-ventilated with fans to lower radon gas concentrations. In the US, the EPA estimates that one in 15 homes has radon levels above the recommended standard.

Oncogenes are genes that are believed make people more susceptible to cancer. Proto-oncogenes are believed to turn into oncogenes when exposed to particular carcinogens. Viruses are also suspected of causing cancer in humans, as this link has already been proven in animals.

Treatment

Treatment for lung cancer depends on the cancer's specific form, how far it has developed, and other factors such as patient details (such as age). Common treatments include surgery, chemotherapy, and radiation therapy.

Radiofrequency ablation is increasing in popularity for this condition as it is nontoxic and causes very little pain. It seems especially effective when combined with chemotherapy as it catches the cells inside a tumor—the ones difficult to get with chemotherapy due to reduced blood supply to the inside of the tumor. It is done by inserting a small heat proble into the tumor to cook the tumor cells. The body then disposes of the cooked cells through its normal eliminative processes.

Surgery is usually not an option for small cell lung cancer. Localized non-small cell lung cancer can be treated surgically. Other curative options for localized non-small cell lung cancer include radiation therapy and radiofrequency ablation treatment.

Small cell lung cancer and locally advanced non-small cell lung cancer are usually treated with a combination of chemotherapy and radiation therapy. If the cancer is metastatic—has spread to distant organs—then the usual treatment is chemotherapy alone.

In recent years, various molecular targeted therapies have been developed for the treatment of advanced lung cancer. Gefitinib is one such drug, however despite an exciting start it was not shown to increase survival and is no longer an active option for lung cancer patients. A new drug called erlotinib has been shown to increase survival in lung cancer patients and has recently been approved by the FDA for second-line treatment of advanced non-small cell lung cancer.[1]

Treatment of non-small cell lung cancer is evolving and the next few years could present exciting developments and new targeted therapies for lung cancer.

Epidemiology

The population segment most likely to develop lung cancer is the over-fifties who also have a history of smoking. Lung cancer is the second most commonly occurring form of cancer in most western countries, and it is the leading cancer-related cause of death for men and women. It is expected that 2001 will have seen 169,500 new cases of lung cancer; 90,700 in men and 78,000 in women. Although the rate of men dying from lung cancer is declining in western countries, it is actually increasing for women due to the increased takeup of smoking by this group.

Prevention

Prevention is the most cost-effective means of fighting lung cancer on the national and global scales. While in most countries industrial and domestic carcinogens have been identified and banned, tobacco smoking is still widespread. Eliminating tobacco smoking should be a primary goal in the fight to prevent lung cancer.

Because prognosis depends heavily on early detection there have been several attempts at secondary prevention. Regular chest radiography and sputum examination programs were not effective in early detection of this cancer and did not result in a reduction of mortality.

External links

Lung Cancer Resources Page at the National Cancer Institute.
Lungs Online – Lung Cancer
Tobacco Smoke and Involuntary Smoking, Summary of Data Reported and Evaluation 2004 by the IARC.
A summary of the previous report by the industry lobbying group GreenFacts.

Categories: Oncology | Pulmonology