(Continued from last week)
Causes of Lung Cancer
Air pollution
Air pollution from vehicles, industry, and power plants can raise the likelihood of developing lung cancer in exposed individuals. Up to 1% of lung cancer deaths are attributable to breathing polluted air, and experts believe that prolonged exposure to highly polluted air can carry a risk for the development of lung cancer similar to that of passive smoking.
What are the types of lung cancer?
Lung cancers, also known as bronchogenic carcinomas (carcinoma is
another term for cancer), 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. These two types of cancers grow and spread in different ways and may have different treatment options, so a distinction between these two types is important.
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 develop lung cancer. Most adenocarcinomas arise in the 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 (3-4 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.
As discussed previously, metastatic cancers from other primary tumors in the body are often found in the lung. Tumors from anywhere in the body may spread to the lungs either through the bloodstream, through the lymphatic system, or directly from nearby organs. Metastatic tumors are most often multiple, scattered throughout the lung, and concentrated in the peripheral rather than central areas of the lung.
What are the signs and symptoms of lung cancer?
Symptoms of lung cancer are varied depending upon where and how widespread the tumor is. Warning signs of lung cancer are not always present or easy to identify. A person with lung cancer may have the following kinds of symptoms:
No symptoms: In up to 25% of people who get lung cancer, the cancer is first discovered on a routine chest X-ray or CT scan as a solitary small mass sometimes called a coin lesion, since on a two-dimensional X-ray or CT scan, the round tumor looks like a coin. These patients with small, single masses often report no symptoms at the time the cancer is discovered.
Symptoms related to the cancer:
The growth of the cancer and invasion of lung tissues and surrounding tissue may interfere with breathing, leading to symptoms such as cough, shortness of breath, wheezing, chest pain, and coughing up blood (hemoptysis). If the cancer has invaded nerves, for example, it may cause shoulder pain that travels down the outside of the arm (called Pancoast’s syndrome) or paralysis of the vocal cords leading to hoarseness. Invasion of the esophagus may lead to difficulty swallowing (dysphagia). If a large airway is obstructed, collapse of a portion of the lung may occur and cause infections (abscesses, pneumonia) in the obstructed area.
Symptoms related to metastasis:
Lung cancer that has spread to the bones may produce excruciating pain at the sites of bone involvement. Cancer that has spread to the brain may cause a number of neurologic symptoms that may include blurred vision, headaches, seizures, or symptoms of stroke such as weakness or loss of sensation in parts of the body.
Paraneoplastic symptoms:
Lung cancers frequently are accompanied by symptoms that result from production of hormone-like substances by the tumor cells. These paraneoplastic syndromes occur most commonly with SCLC but may be seen with any tumor type. A common paraneoplastic syndrome associated with SCLC is the production of a hormone called adrenocorticotrophic hormone (ACTH) by the cancer cells, leading to oversecretion of the hormone cortisol by the adrenal glands (Cushing’s syndrome). The most frequent paraneoplastic syndrome seen with NSCLC is the production of a substance similar to parathyroid hormone, resulting in elevated levels of calcium in the bloodstream.
Nonspecific symptoms:
Nonspecific symptoms seen with many cancers, including lung cancers, include weight loss, weakness, and fatigue. Psychological symptoms such as depression and mood changes are also common.
When should one consult a doctor?
One should consult a health-care provider 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, and/or breathing difficulties such as shortness of breath or wheezing.
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