Malignant mesothelioma is a tumour originating from mesothelial cells. 85–95% of mesotheliomas are caused by asbestos exposure. It occurs much more commonly in the chest (malignant pleural mesothelioma) than in the abdomen (peritoneal mesothelioma). Rarely mesothelioma arises in the pericardium or tunica vaginalis testis, the membrane surrounding the testicles.
It is accepted by all expert bodies including the World Health Organisation that all types of asbestos cause mesothelioma. Crocidolite (blue asbestos) carries the highest risk, amosite (brown asbestos) is almost as dangerous, and chrysotile (white asbestos) the least dangerous.
Some of the cases which arise in patients who cannot recall any asbestos exposure probably result from unidentified occupational or domestic exposure. Many cases have occurred in families of workers exposed to asbestos who carried the dust home on their clothes and hair. Other cases probably arise as a result of contamination of the air by asbestos fibres released from asbestos in the environment.
A few cases probably occur spontaneously unrelated to any asbestos exposure. Any type of cancer can arise spontaneously as a result of accidental genetic mutations
In the UK, there are now around 2500 mesothelioma deaths a year, expected to stay around this level until the end of the decade before a slow decline. Mortality is beginning to decline in younger men but overall is expected to increase by 10-20% over the next 5-10 years, then to fall gradually. Mesothelioma may occur after a small exposure to asbestos but the risk increases with the amount of asbestos exposure. The usual interval between first exposure to asbestos and death from mesothelioma is around 40 (30-50) years but may be as little as 10 years or as much as 60 years or more.
The risk of mesothelioma is not affected by smoking.
Presentation and Diagnosis
Patients with pleural mesothelioma usually present to their doctor with chest pain and/or breathlessness.
Usually, there is a pleural effusion (i.e. fluid in the chest cavity) accounting for the breathlessness. They may have a cough, feel tired and generally unwell.
Chest X-rays and CT scans often lead to a strong suspicion of mesothelioma. It is necessary to take samples of tissue (a biopsy) from the tumour or fluid from the pleural cavity for examination under the microscope in order to confirm the diagnosis.
The samples can often be obtained by passing a special needle through the skin of the chest. This is often done with help from an ultrasound scan or CT scan to make sure the most appropriate area is sampled.
These procedures are done under local anaesthesia. Sometimes these methods do not give the diagnosis. It is then necessary to perform a small operation known as a thoracoscopy or pleuroscopy.
This is done under general anaesthesia or sometimes under local anaesthesia. It involves small incisions in the chest between the ribs to allow a viewing telescope and forceps to be passed into the chest. The surgeon can see the tumour and take samples from it.
When the samples have been obtained the pathologist looks at them under the microscope and performs special stains to identify the tumour as a mesothelioma and to determine the type of mesothelioma. This often takes a week or more.
The principal histological varieties are epithelioid, sarcomatoid and mixed. Patients with the epithelioid type tend to survive a little longer. The median survival from presentation is 12–18 months; a few patients with epithelioid tumours survive for more than 5 years. It is important to appreciate that these are average figures and should not be taken as predictions of life expectancy for an individual patient without consideration of the particular circumstances of that patient.
Source: Dr Robin Rudd, MA MD FRCP, Consultant Oncologist: Reviewed by Dr Robin Rudd: March 2017