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Definition
Malignant mesothelioma (MM) is a rare, insidious cancer of the lining surfaces of the lung, abdomen and heart.
Comments
- It is strongly associated with previous asbestos exposure.
- There is no known effective treatment, though several regimes may be tried.
- The average survival rate, regardless of which form of treatment is used, is 18 months from diagnosis. Without treatment, the average survival rate is 6 months.
- Most (80%) of mesotheliomas involve the lung lining (pleura), and the rest are found in the lining membrane of the abdomen (peritoneum) or heart (pericardium)
- Men are affected more often than women, usually during late middle age.
Causes
Asbestos exposure
The vast majority (70%) of pleural and peritoneal MMs have had documented exposure to inhaled asbestos fibres. However, symptoms may not appear for 20 - 30 years after initial exposure
Previous irradiation
There is no clear-cut proof, but it is thought that radiation therapy for Hodgkin's lymphoma may trigger the later onset of MM of the pleura. The data for breast cancer irradiation is less clear.
Viruses
The Simian Virus may cause cancer in humans by inactivating tumour suppressor genes. This is a theoretic more than practical consideration.
Symptoms and usage
MM of the pleura most commonly causes chest pain and shortness of breath, and in advanced cases, cough, anaemia, and weight loss. Blood may be coughed up or a lung may collapse. Examination shows signs of fluid in the chest cavity, usually on one side only.
Peritoneal MM causes symptoms only at a late stage, and these may include pain, abnormal bowel function and weight loss. A tumour may be felt in the abdomen, or there may be excess fluid (ascites) present.
Spread of the tumour is not common, but can happen via the blood to liver, bone and adrenal glands.
Regardless of the primary site, MM can cause generalised problems, such as
- Jaundice
- Clots in the veins, leading to
- Pulmonary emboli (vein clots breaking off and lodging in the lung arteries)
Diagnosis and investigations
There is a long delay between asbestos exposure and MM. In addition, the symptoms can be vague and easily attributed to more common disorders. For these reasons, MM is often misdiagnosed or not even considered at first presentation to the doctor.
Chest X-ray may show the tumour/s and pleural effusion (fluid). Scans (CT or MRI) may give clearer, more detailed images if there is any doubt, and will show involvement of lymph glands and any invasion into nearby structures.
Sampling the pleural fluid or the pleura itself, is a logical step. However, even this may be problematic. The process of obtaining the samples, by inserting a needle, drain or endoscope, brings a high risk of spreading the cancer along the tract formed when the instrument is inserted: the malignant cells travel along the tract and reach the skin, where they grow into secondary tumours.
Treatment
Treatment of the MM itself is not successful, although there have been a notable few who have survived for several years.
Pain relief is mandatory.
Collections of malignant fluid around the lung, heart and intestines may be drained for the patient's comfort, but tend to re-accumulate quickly. In the chest it is possible to do a talc pleurodesis: this process introduces talc into the pleural space, causing such a chemical irritation that the lung and chest wall pleura eventually stick to each other. This obliterates the pleural space, leaving nowhere for the malignant fluid to collect. It is not often successful, and is a painful procedure, and is therefore not often recommended.
Surgery to remove the thick layer of tumour over the lung, or even removal of the lung itself, and/or part of the diaphragm has been tried without much success. In some cases surgery is just not possible.
MM is not sensitive to chemotherapy or radiotherapy, but some small increased survival has been achieved in a few selected patients, using a combination of these before and after surgery.
Immunotherapy has been equally unsuccessful.
Dr. AG Hall
