Mesothelioma developes in approximately 3,000 United States citizens every year. Most of those diagnosed have a history of occupational exposure to asbestos, though a few have environmental or household contact. This cancer has an extremely long latency period; an exposure period of as little as one or two months can result in a mesothelioma up to 50 years later. Patients who had contact with asbestos as far back as the 1940s are now being diagnosed with this disease. In fact, the average time between exposure and the development of mesothelioma is 35-40 years.
When asbestos first came into use, its risks were unknown, and it was widely used as a fire-retardant material. Many people worked with this deadly substance, unaware that it would kill them several decades later. Workers such as bricklayers, insulaters, plasterers, electricians, mechanics, carpenters, and other tradesmen were exposed to asbestos on a daily basis as it was contained in many insulation and construction materials.
Even occassional exposure to asbestos is a health risk, and there have been many cases of mesothelioma developing in patients who only had brief contact, such as wives of asbestos-exposed workers who washed their husbands' overalls.
Due to the long latency period and vague, diffuse initial symptoms, there is often a delay in accurate diagnosis. As with many cancers, early symptoms can be mild and non-specific. Often patients present with only shortness of breath and a persistent cough; some show no symptoms at all in the initial stages, and the disease is first noticed on a routine chest X-ray.
One early tell-tale sign is pleural effusion, a collection of fluid in the lungs. The right lung is affected 60% of the time, bilateral involvement being seen in 5% of cases. Less common initial complaints due to lung mesothelioma are fever, night sweats, weight loss, a raspy voice and facial swelling. Peritoneal mesothelioma can cause abdominal symptoms such as pain, abdominal swelling, nausea, weight loss, bowel obstruction, anemia and swelling of the feet. As the disease progresses, patients often develop severe cachexia (wasting).
One of the most common symptoms of mesothelioma, pleural effusion, is an accumulation of fluid between the parietal pleura, which covers the chest wall and diaphragm, and the visceral pleura, which covers the lungs. Both membranes are covered with mesothelial cells which, under normal conditions, produce a small amount of fluid that acts as a lubricant between the chest wall and the lung. Any excess fluid is removed via blood and lymph vessels, thus maintaining a balance. When more fluid is produced than can be absorbed, an effusion forms.
These effusions are called either transudates and exudates. A transudate is a clear fluid that forms not because the pleural surfaces are diseased, but because of an imbalance between the normal production and removal of the fluid. Often this is caused by congestive heart failure. An exudate, which contains many cells and proteins and is often cloudy in color, results from disease of the pleura itself, and is common to mesothelioma. To differentiate between a transudate or an exudate, a diagnostic thoracentesis, in which a needle or catheter is used to obtain a fluid sample, may be conducted.
As the volume of excess fluid increases, symptoms develop such as shortness of breath (dyspnea) , chest pain, or a non-productive dry cough. Heard through a stethoscope, normal breath sounds are muted, and tapping on the chest will reveal dull rather than hollow sounds.
A pleural effusion can be seen with a chest X-ray, ultrasound or CT scan. Since pleural effusions are often caused by congestive heart failure, the discovery of an effusion is not in itself immediately suggestive of a malignant process.
A histological examination of pleural fluid is negative in 85% of cases; a definitive diagnoses is more often is obtained by a needle biopsy or surgical biopsy of pleural tissue.
Symptomatic treatment of lung compression caused by effusion is accomplished by application of a sclerosing agent which eliminates the space between the lung and the chest cavity, a process called chemical pleurodesis. Talc is usually used, with a success rate of 95%. It can be administered either as a powder or as a slurry mixed with saline.
A surgical team opens the chest wall, removes the effusion, then collapses the lung before applying the talc. Once the lung is fused to the chest wall, an effusion can no longer accumulate and compress the lung. This is strictly a palliative measure to improve the patient's quality of life, and has no effect on the progression of the disease.
Attemps to cure mesothelioma utilize surgery to remove diseased tissue, combined with chemo and raiotherapy. Several new treatment modalities are currently being investigated. These include Photodynamic therapy, which uses light of particular frequencies to target and kill cancer cells which, compared to normal tissue, display increased uptake of photosensitizing drugs; immunotherapy, which fights the abnormal cells through stimulation of the body's own immune system; and Intensity Modulated Radiation Therapy, which is a radiation treatment that attempts to target just the malignancy, thus avoiding damage to adjacent healthy cells and tissue. In addition, some success has been acheived with the chemotherapeutic drug Alitma (pemetrexed). However, despite the number of clinical trials currently underway, as of the date of this article the prognosis for mesothelioma sufferers is still extremely poor.