Mesothelioma- the silent killer

Mesothelioma is a rare form of cancer in which malignant (cancerous) cells are found in the mesothelium, a protective sac that covers most of the body’s internal organs.

Mesothelioma is a form of cancer that is almost always caused by previous exposure to asbestos.Its most common site is the pleura (outer lining of the lungs and chest cavity), but it may also occur in
the peritoneum (the lining of the abdominal cavity) or the pericardium(a sac that surrounds the heart).

They are invasive and can damage nearby tissues and organs. Cancer cells can also metastasize (spread) from their original site to other parts of the body.

The mesothelium is a membrane that forms the lining of several body cavities:

• the pleura (thoracal cavity),
  
• peritoneum (abdominal cavity)
  
• and pericardium (heart sac).
  

• male internal reproductive organs (the tunica vaginalis testis)
• and covers the internal reproductive organs of women (the tunica serosa uteri).

The mesothelium has different names, depending on its location in the body. The peritoneum is the mesothelial tissue that covers most of the organs in the abdominal cavity. The pleura is the membrane that surrounds the lungs and lines the wall of the

Although reported incidence rates have increased in the past 20 years, mesothelioma is still a relatively rare cancer. The incidence is approximately one per 1,000,000.

For comparison, populations with high levels of smoking can have a lung cancer incidence of over 1,000 per 1,000,000. Incidence of malignant mesothelioma currently ranges from about 7 to 40 per 1,000,000 in industrialized Western nations, depending on the amount of asbestos exposure of the populations during the past several decades.

It has been estimated that incidence may have peaked at 15 per 1,000,000 in the United States in 2004. Incidence is expected to continue increasing in other parts of the world.

Mesothelioma occurs more often in men than in women and risk increases with age, but this disease can appear in either men or women at any age. Approximately one fifth to one third of all mesotheliomas are peritoneal. Between 1940 and 1979, approximately 27.5 million people were occupationally exposed to asbestos in the United States.

Between 1973 and 1984, there has been a threefold increase in the diagnosis of pleural mesothelioma in Caucasian males. From 1980 to the late 1990s, the death rate from mesothelioma in the USA increased from 2,000 per year to 3,000, with men four times more likely to acquire it than women.

Working with asbestos is the major risk factor for mesothelioma. Asbestos is a natural mineral, mined from rock found in many countries. It is made up of tiny fibres that are as strong as steel but can be woven like cotton and are highly resistant to heat and chemicals.

There are three main types of asbestos :

• blue (crocidolite),
  
• brown (amosite)
  
• and white (Chrysotile).

A history of asbestos exposure exists in almost all cases. It is reported in about 70 percent to 80 percent of all cases. Mesothelioma does not usually develop until many years after exposure to asbestos. It can take any time from 10 to 60 years, although the average is about 30 to 40 years after exposure to asbestos.

However, mesothelioma has been reported in some individuals without any known exposure to asbestos e.g. In rare cases, mesothelioma has also been associated with :

• irradiation,
  
• intrapleural thorium dioxide (Thorotrast),
  
• and inhalation of other fibrous silicates, such as erionite.
  

Asbestos has been widely used in many industrial products. However, if tiny asbestos particles float in the air, especially during the manufacturing process, they may be inhaled or swallowed, and can cause serious health problems.

In addition to mesothelioma, exposure to asbestos increases the risk of lung cancer, asbestosis (a noncancerous, chronic lung ailment), and other cancers, such as those of the larynx and kidney. Smoking does not appear to increase the risk of mesothelioma. However, the combination of smoking and asbestos exposure significantly increases a person’s risk of developing cancer of the air passageways in the lung.

Asbestos has been mined and used commercially since the late 1800s. Its use greatly increased during World War II. Since the early 1940s, millions of American workers have been exposed to asbestos dust. Initially, the risks associated with asbestos exposure were not known.

However, an increased risk of developing mesothelioma was later found among shipyard workers, people who work in asbestos mines and mills, producers of asbestos products, workers in the heating and construction industries, and other trades people.

Working with asbestos is the major risk factor for mesothelioma. A history of asbestos exposure exists in almost all cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos. In rare cases, mesothelioma has also been associated with :

• irradiation,
• intrapleural thorium dioxide (Thorotrast),
  
• and inhalation of other fibrous silicates, such as erionite

Exposure to asbestos fibres has been recognised as an occupational health hazard since the early 1900s. The risk of asbestos-related disease increases with heavier exposure to asbestos and longer exposure time. However, some individuals with only brief exposures have developed mesothelioma. On the other hand, not all workers who are heavily exposed develop asbestos-related diseases.

There is some evidence that family members and others living with asbestos workers have an increased risk of developing mesothelioma, and possibly other asbestos-related diseases. This risk may be the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers. To reduce the chance of exposing family members to asbestos fibers, asbestos workers are usually required to shower and change their clothing before leaving the workplace.

Many building materials used in both public and domestic premises prior to the banning of asbestos may contain asbestos. This greatly increases the incidence of mesothelioma occurrence. However, Incidence of mesothelioma also had been found to be higher in populations living near naturally occuring asbestos. This shows the influence of environmental exposures to occurrence of this fatal disease.

The 3 major histological types of mesothelioma are

• sarcomatous,

• epithelial,

• mixed.
  

The tumor may also grow along drainage and thoracotomy tracts. As the disease progresses, it often extends into the pulmonary parenchyma, chest wall, and mediastinum. Pleural mesothelioma may extend into the

• esophagus,
• ribs,
• vertebra,
• brachial plexus,
• and superior vena cava.

This is the result in the penetration of the visceral pleura from where the fibre can then be carried to the pleural surface, thus leading to the development of malignant mesothelial plaques.

The processes leading to the development of peritoneal mesothelioma remain unresolved, although it has been proposed that asbestos fibres from the lung are transported to the abdomen and associated organs via the lymphatic system.

It is also believed that the development of peritoneal mesothelioma is proposed to have been result from asbestos fibres being coughed up and swallowed. Additionally, asbestos fibres may be deposited in the gut after ingestion of sputum contaminated with asbestos fibres.

In detail investigation, the development of mesothelioma in rats has been demonstrated following intra-pleural inoculation of phosphorylated chrysotile fibres. It shows that smaller particles may be more dangerous than the larger fibers.

It is believed that in humans, transport of fibres to the pleura is critical to the pathogenesis of mesothelioma. After the penetration there is evidence of recruitment of significant numbers of macrophages and other cells of the immune system to localised lesions of accumulated asbestos fibres. As the disease progressed, these lesions continued to attract and accumulate macrophages and cellular changes. Then eventually, within the lesion culminated in a morphologically malignant tumour.

Symptoms of mesothelioma may not appear until 20 to 50 years after exposure to asbestos. The symptoms and complain of patient is actually depend on the location of the disease.

In the early stages when the mesothelioma is present as small lumps it will not show up on any scans or x-rays and is unlikely to cause any symptoms. As it progresses, we can see some general symptoms such as sweating, tiredness, loss of appetite and weight loss. Usually it will start up with affection of the pleural cavity.
Pleural mesothelioma :

• Shortness of breath,
  
• cough,
  
• and pain in the chest due to an accumulation of fluid in the pleural space
  

• chest wall pain pleural effusion,
  
• or fluid surrounding the lung
  
• shortness of breath
  
• fatigue
  
• or anemia
  
• wheezing,
  
• hoarseness,
  
• or cough blood in the sputum
  
• The individual may develop a pneumothorax, or collapse of the lung.

• weight loss and cachexia,
  
• abdominal swelling
  
• and pain due to ascites
  
• bowel obstruction,
  
• blood clotting abnormalities,
• anemia,
  
• and fever.
  

• pain,
  
• trouble swallowing,
  
• or swelling of the neck or face.

• blood clots in the veins, which may cause thrombophlebitis
  
• disseminated intravascular coagulation
  
• jaundice,
• low blood sugar level pleural effusion
  
• pulmonary emboli,
  
• severe ascites
  

Diagnosis begins with a review of the patient’s medical history, especially history of asbestos exposure. A complete physical examination may be performed. After that some further scanning test are used :

• x-rays of the chest or abdomen
  
• ung function tests.
  
• CT (or CAT) scan
  
• or an MRI

Treatment for mesothelioma depends on:

• location of the cancer,
  
• the stage of the disease,
  
• and the patient’s age
  
• and general health.
  

• surgery,
  
• radiation therapy,
  
• and chemotherapy.
  

1. Surgery is a common treatment for mesothelioma. This is an operation in which the doctor may remove part of the lining of the chest or abdomen and some of the tissue around it. E.g. for pleural mesothelioma, pneumonectomy is performed (a part or the whole lung is removed). Sometimes part of the diaphragm, the muscle below the lungs that helps with breathing, is also removed.It can be divided to two types of surgery. Radical surgery and palliative surgery.
2. Radiation therapy is a treatment involves the use of high-energy rays to kill cancer cells and shrink tumors. The radiation may come from a machine (external radiation) or from putting materials that produce radiation through thin plastic tubes into the area where the cancer cells are found (internal radiation therapy).
3. Chemotherapy is the use of anticancer drugs to kill cancer cells throughout the body. Most drugs used to treat mesothelioma are given by injection into a vein (intravenous, or IV). Sometimes, the doctor may use a needle or a thin tube to drain fluid that has built up in the chest or abdomen. This is done on the purpose of relieving symptoms and control pain.