Lung cancer kills more men and women than any other form of cancer. It is estimated that by the year 2000, over three hundred thousand people will die from lung cancer in the United States alone. The economic loss is calculated to be over two billion dollars a year.
Most lung cancers begin to grow silently, without any symptoms. Patients with lung cancer often do not develop symptoms until the cancer is in an advanced stage. The actual time from when one cell becomes cancerous until it is large enough to be diagnosed or produce symptoms may take as long as 10 to 40 years. Since the majority of lung cancer is diagnosed at a relatively late stage, only 10% of all lung cancer patients are ultimately cured. If the patient cannot be cured by surgery at the time the cancer is found, there is a 50% chance that death will occur in less than one year.
WHAT ARE CAUSES OF LUNG CANCER?
Smoking: 90% of patients with lung cancer have a smoking history. There is a direct relationship between amount of tobacco exposure and risk for developing lung cancer. Stopping smoking is associated with a gradual decrease in risk, but an appreciable diminution of riskoccurs only after a long period of time(more than 6 months).
Occupational and atmospheric pollution: Exposure to agents such as arsenic, asbestos, beryllium, chloromethylethers, mustard gas and radiation has been linked with development of lung cancer.
Inhalation of combustion byproducts: In Asians, the population of cases attributable to active smoking may not be as high. The rate of deaths from smoking-related lung cancer has been reported to be as low as 6% among Asian women, however, an additional lung cancer risk unrelated to smoking has been observed among Chinese women. No smoking risk factors in these patients include inhalation of combustion byproducts from cooking, heating stoves, and oil furnaces.
The risk of lung cancer is greater for those living in urban areas. This risk is approximately 1.2 to 2.3 times that of people living in rural areas. There is also an increased risk of lung cancer in smokers whose close relatives have had lung cancer. Scarring in the lungs from previous infections or injury can be associated with and increased risk of cancer.
WHAT ARE TYPES OF LUNG CANCER?
Lung cancers are broadly classified into small cell or non-small cell. Non-small cell cancers are further divided into adenocarcinomas, bronchoalveolar-alveolar, squamous cell and large cell carcinomas. Approximately, 75-85 percent of lung cancers are non-small cell cancers and 15-25 percent are small cell cancers of the lung.
Non-Small Cell Cancer of the Lung
Adenocarcinoma is the most common non-small cell cancer of the lung. The majority of these cancers develop in the periphery (outer part) of the lung. Since these cancers are in the outer portion of the lung, the patient often does not have any symptoms when the cancer is found on a chest x-ray. Adenocarcinomas tend to metastasize (spread to other parts of the body) to the bone, the central nervous system (the brain and spinal cord), the adrenal glands, the liver, and the opposite lung.
Frequently, there is scarring in adenocarcinomas. Sometimes, the cancer arises in an area of old scarring of the lung. In other cases, the scar appears to arise secondary to the growth of the cancer.
Bronchoalveolar carcinoma or alveolar cell carcinoma is a non-small cell carcinoma that can be found throughout the respiratory tract. When it is discovered as a single mass on a patient's x-ray, this type of lung cancer has an excellent prognosis. Five year survival after surgery is in the 75-90 percent range. If, however, it is found in its diffuse form (meaning it has spread beyond a single mass), the prognosis is quite poor.
Squamous cell carcinomas comprise 30-40 percent of non-small cell carcinomas of the lung. This type of cancer tends to be located in the more central portion of the lung. Often, this is in a bronchus (a large airway of the lung). Since these cancers are located near or in these airways, they can cause symptoms earlier in their growth. Coughing and production of phlegm (sputum) that is bloody are common symptoms. The cancer can block airways which can lead to shortness of breath orpneumonia.
Large cell carcinomas represent about 10 percent of non-small cell cancers of the lung. This form of lung cancer has fewer structural characteristics when viewed under a microscope. It is sometimes difficult to distinguish this form of lung cancer from cancers which have spread to the lung from another place in the body.
Small Cell Cancer of the Lung
Small cell cancer is the most aggressive type of lung cancer and has the worst prognosis. These cancers tend to grow rapidly and metastasize to other parts of the body early.
Small cell cancer of the lung is usually seen as a mass located in the central portion of the chest on chest x-ray. The primary cancer spreads to lymph nodes of the chest and also enters the blood stream which carries it to other organs such as the liver, bone, brain and spinal cord, kidneys, pancreas, and adrenal glands.
It is rare that small cell cancer of the lung can be cured with surgery because either the primary cancer is too large to be removed or it has already spread to other parts of the body. However, small cell cancer of the lung is generally quite responsive to radiation therapy and chemotherapy.
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