What Causes Small Cell Lung Cancer?
Signs & Symptoms
Limited vs. Extensive Stage
What is Small Cell Lung Cancer?
The 20th century has witnessed an increase in lung cancer of epidemic proportions. Worldwide, it is estimated that over one million people will be diagnosed with lung cancer this year. This discussion will focus on the diagnosis and evaluation of one specific type of lung cancer known as small cell lung cancer.
Lung cancers arise from the lungs or the bronchi (the tubes through which air passes to and from the lungs). Our lungs are essential to life, though we can sometimes live with just one lung as long as it is fairly healthy.
Lung cancers are divided into two groups depending upon what they look like under the microscope: non-small cell lung cancer and small cell lung cancer (also known as "oat cell" cancer). The two groups of lung cancer behave differently with respect to the way they grow and spread and the way they respond to various forms of treatment. About 1 out of every 5 cases of lung cancer is the small cell type.
Small cell lung cancer is a very aggressive form of lung cancer. People with small cell lung cancer who do not receive treatment on average live only several months from the time of their diagnosis of cancer. Compared with non-small cell lung cancer, small cell lung cancer tends to spread (metastasize) early. At the time of their diagnosis, many patients are found to have disease that has already spread. For this reason, local forms of cancer treatment like surgery and radiation therapy when used alone are ineffective. The development of chemotherapy which when given either by mouth or through a vein goes to all parts of the body has significantly increased the life expectancy and improved the outlook for patients with small cell lung cancer.
What Causes Small Cell Lung Cancer?
Researchers say that the single most important preventable cause of small cell lung cancer is tobacco smoking (smoking is also linked with non-small cell lung cancer, head and neck cancer, and cancers of the esophagus, stomach and bladder). Over one hundred different cancer-causing substances have been found in cigarette smoke. Recently, we have learned that people who do not smoke but are regularly exposed to the cigarette smoke of others (second hand smoke) are also at risk for developing cancer. Exposure to radon, a colorless, odorless, radioactive gas that is frequently found in the basements of poorly ventilated buildings is also associated with small cell lung cancer.
Cancer promoting substances cause changes in the normal cell DNA, known as mutations. Accumulation of specific combinations of these mutations can transform the cell into a cancer that grows uncontrollably. Why some smokers develop lung cancer and others do not is not yet clear. Hereditary factors may be as important as environmental exposure to carcinogens.
Small cell lung cancer is thought to arise from a special lung cell called the Kulchitsky cell. Since this cell is present in the larger airways, small cell lung cancer often occurs in this location. Compared with non-small cell lung cancer, small cell lung cancer tends to invade deeper into the airway earlier in the course of the disease, which may be the reason why it tends to spread to distant sites (or metastasize) early.
As with most other cancers, the initial signs and symptoms of small cell lung cancer depend upon the location and size of the tumors. Typically, the primary tumor arises in the central lung where it can block the airways and cause coughing (the cough may be dry or produce phlegm and/or blood), shortness of breath, wheezing, and chest pain. Extension of the cancer into the center of the chest can lead to compression of the major blood vessels, which may cause swelling of the face and arms. Blockage of a major airway can cause a life-threatening type of pneumonia. Small cell lung cancer can also produce hoarseness of the voice by invading nerves that control the vocal cords.
By the time the diagnosis of small cell lung cancer is made, spread of the cancer to distant organ systems (known as metastasis; plural is metastases) has frequently already occurred. Patients may or may not have symptoms from distant metastases. Brain metastases may cause headaches or neurological symptoms like seizures, loss of strength or control of a limb and problems walking. Spread of the cancer to the liver may cause abdominal pain or jaundice, an abnormal yellowing of the skin and eyes. Bone metastases may cause pain, fractures or decreased blood counts (because certain bones produce blood cells). Spread of the cancer to the spine can lead to spinal cord compression, which may cause pain, paralysis, or incontinence (inability to control urine and feces excretion).
Small cell lung cancer is sometimes associated with other health problems due to substances produced by the cancer cells. These include syndrome of inappropriate antidiuretic hormone, which causes low sodium in the blood, and Eaton-Lambert syndrome which causes weakness in the arms and legs. Weight loss is also a common finding among patients with small cell lung cancer.
Limited vs. Extensive Stage
In order to make decisions about treatment we must know where the cancer is located and how much cancer is present. This is known as the stage of the cancer. Small cell lung cancer has a stage system different from other lung cancers. A simple two-stage system is commonly used for small cell lung cancer. Limited stage refers to cancer confined to one lung and nearby lymph nodes (small glands found throughout the body that produce cells involved in the immune system). Extensive stage applies to cancer that has spread beyond the definition of limited stage. Recurrent stage means that the cancer has come back after it has been treated. Small cell lung cancer may recur either in the lungs or in another part of the body.
In order to learn the extent of disease a full evaluation needs to be performed. The most important components of the evaluation are the medical history interview and physical examination, which provide vital information not only about the extent of disease but also about the patient's general health and other pre-existing conditions that may influence how well the patient tolerates the various treatment options.
Just like lung cancer can spread to other parts of the body, cancers of other parts of the body can metastasize to the lungs. Therefore, it is important to distinguish whether a tumor found in the lung represents a primary lung cancer (a cancer that started in the lungs) or a metastasis from another site. Most of the time, a sample of the cancer tissue (known as a biopsy) provides a straightforward answer.
The primary tumor and any spread of the cancer are first evaluated by looking at the chest with an x-ray or CAT scan (a special, more detailed x-ray that shows cross-sections of the body). Fiberoptic bronchoscopy (a procedure performed by lung specialists called pulmonologists which involves passing a flexible tube through the mouth and into the lungs to examine the airways) is often commonly done. If the tumor is seen during the bronchoscopy, a biopsy can be performed, which involves using a needle is to remove a small piece of the tumor. This piece of tumor is then studied under the microscope to identify the type of cancer.
If the tumor is not seen during bronchoscopy, another way of obtaining a biopsy is by using a CAT scan-guided biopsy. This procedure involves inserting a long, thin needle into the chest and directing it into the tumor using the CAT scan for guidance. Distant metastases that cannot be biopsied are identified and evaluated by analyzing blood samples and getting special x-rays. This may include a CAT scan or MRI scan (a test like the CAT scan which shows detailed cross-sections of the body, but uses magnetic waves instead of x-rays to make the images), a bone scan (a special x-ray test that looks for cancer in the bones), and/or a bone marrow biopsy (which involves inserting a needle into either the hip or back). Your doctor will advise you on which of these tests you need.
Depending on the results of the biopsy and x-rays, pulmonary function testing, which assesses the condition of the lungs, may be done. This testing is performed to ascertain whether the patient has sufficient lung function to tolerate surgery or radiation therapy. If surgery is being contemplated as a treatment option, the patient also undergoes an EKG (heart tracing) and often needs to be seen by a heart specialist, who may recommend additional tests to evaluate heart function.
The factors that consistently increase the likelihood of prolonged survival include good overall health, female gender, and limited cancer spread. People with involvement of the brain or liver at the time of diagnosis have a significantly worse outcome. Patients are encouraged to stop smoking before initiation of treatment. Smoking causes irritation of the airways, further compromises lung function and deprives the body of oxygen, which is needed for the tumor-killing effects of chemotherapy and radiation.
At the time of diagnosis, roughly 2 of every 5 patients with small cell lung cancer have limited stage disease. The average survival for limited stage disease is 16 to 24 months with current forms of treatment. Though these statistics may seem grim, it is important to remember that limited stage disease is potentially curable. Recent studies suggest that about 25% of patients survive five or more years using the most current therapies. The average survival is 6 to 12 months among patients with extensive stage disease; long term survival is, unfortunately, rare.