Mesothelioma- the silent killer

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).

image from www.enviraz.co.uk/about_asbestos.htm



They are all harmful but blue and brown asbestos are recognised as the most hazardous.

Most people with malignant mesothelioma have worked on jobs where they breathed asbestos. Others have been exposed to asbestos in a household environment, often without knowing it.

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.
  

Some studies also suggest that simian virus 40 (SV40) may act as a cofactor in the development of mesothelioma.

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.
  

Pleural mesothelioma usually begins as discrete plaques and nodules that coalesce to produce a sheetlike neoplasm. Tumor growth usually begins at the lower part of the chest. Deposits of asbestos fibres deep in the base of the lungs may result in these fibres penetrating through into the pleural membranes where the fibre can then be carried to the pleural surface, then it may invade the diaphragm and encase the surface of the lung and interlobar fissures.

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
  

Besides, it also can cause these signs and symptoms:

• 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.

Pleural tumors usually will affect unilaterally.

Tumors that affect the abdominal cavity often do not cause symptoms until they are at a late stage. It affects the peritoneal cavity.
peritoneal mesothelioma :

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

If the cancer has spread beyond the mesothelium to other parts of the body, symptoms may include :

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

In severe cases of the disease, the following signs and symptoms may be present:

• 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

A biopsy is needed to confirm a diagnosis of mesothelioma. So, how biopsy is done?
In a biopsy, a surgeon or a medical oncologist removes a sample of tissue for examination under a microscope by a pathologist.
A biopsy may be done in different ways, depending on where the abnormal area is located e.g. if the cancer is in the chest, the doctor may perform a thoracoscopy, if the cancer is in the abdomen, the doctor may perform a peritoneoscopy.

The stages of the disease is important if the obtaining result is mesothelioma. Staging involves more tests in a careful attempt to find out whether the cancer has spread and, if so, to which parts of the body. This is especially important in planing the treatment.
It can be classified as localised or advanced if it has spread beyond the original membrane surface to other parts of the body, such as the lymph nodes, lungs, chest wall, or abdominal organs.

Treatment for mesothelioma depends on:

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

Standard treatment options include :

• 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.
   

Besides, there's also symptomatic treatment. This kind of treatment can't help curing the disease but just to relieve any complication or discomfort caused by the disease itself. Such of this is, pleurocentesis-by drainage of the fluid accumulating in between the pleural cavity. Some others may include antiemetic drug to stop nausea and vomiting, analgesic to relieve pain and etc.