Mesothelioma or more precisely, malignant mesothelioma) is a rare form of cancer that develops from cells of the mesothelium, the protective lining that covers many of the internal organs of the body.

Mesothelioma is most commonly caused by exposure to asbestos.

The most common anatomical site for mesothelioma is the pleura (the outer lining of the lungs and internal chest wall), but it can also arise in the peritoneum (the lining of the abdominal cavity), the pericardium (the sac that surrounds the heart), or the tunica vaginalis (a sac that surrounds the testis).

Most people who develop mesothelioma have worked in jobs where they inhaled or ingested asbestos fibers, or were exposed to airborne asbestos dust and fibers in other ways.

Washing clothes of a family member who worked with asbestos also creates a risk for developing mesothelioma.

Unlike lung cancer, there seems to be no association between mesothelioma and tobacco smoking, but smoking greatly increases the risk of other asbestos-induced cancers.

Signs and symptoms of mesothelioma include shortness of breath due to pleural effusion (fluid between the lung and the chest wall), chest wall pain and constitutional signs such as unexplained weight loss.

The diagnosis may be suspected based on chest X-ray and CT scan findings but must be confirmed either by examining serous effusion cytology or with a biopsy (removing a sample of the suspicious tissue).

A thoracoscopy (inserting a tube with a camera into the chest) can be used to acquire biopsy material and allows the introduction of substances such as talc to obliterate the pleural space (a procedure called pleurodesis), preventing more fluid from accumulating and pressing on the lung.

Despite treatment with chemotherapy, radiation therapy or sometimes surgery, mesothelioma carries a poor prognosis. Research about screening tests for the early detection of mesothelioma is ongoing.

Signs and symptoms

Symptoms or signs of mesothelioma may not appear until 20 to 50 years (or more) after exposure to asbestos. Shortness of breath, cough, and pain in the chest due to an accumulation of fluid in the pleural space (pleural effusion) are often symptoms of pleural mesothelioma.

Symptoms of peritoneal mesothelioma include weight loss and cachexia, abdominal swelling and pain due to ascites (a buildup of fluid in the abdominal cavity).

Other symptoms of peritoneal mesothelioma may include 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, a disorder causing severe bleeding in many body organs
Jaundice, or yellowing of the eyes and skin
Low blood sugar level
Pleural effusion
Pulmonary emboli, or blood clots in the arteries of the lungs
Severe ascites

A mesothelioma does not usually spread to the bone, brain, or adrenal glands. Pleural tumors are usually found only on one side of the lungs.

Cause

Working with asbestos is the major risk factor for mesothelioma. In the United States, asbestos is the major cause of malignant mesothelioma and has been considered “indisputably” associated with the development of mesothelioma.

Indeed, the relationship between asbestos and mesothelioma is so strong that many consider mesothelioma a “signal” or “sentinel” tumor.

A history of asbestos exposure exists in most 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.

Diagnosing mesothelioma is often difficult because the symptoms are similar to those of a number of other conditions. Diagnosis begins with a review of the patient’s medical history. A history of exposure to asbestos may increase clinical suspicion for mesothelioma.

A physical examination is performed, followed by chest X-ray and often lung function tests. The X-ray may reveal pleural thickening commonly seen after asbestos exposure and increases suspicion of mesothelioma. A CT (or CAT) scan or an MRI is usually performed.

If a large amount of fluid is present, abnormal cells may be detected by cytopathology if this fluid is aspirated with a syringe. For pleural fluid, this is done by thoracentesis or tube thoracostomy (chest tube); for ascites, with paracentesis or ascitic drain; and for pericardial effusion with pericardiocentesis.

While the absence of malignant cells on cytology does not completely exclude mesothelioma, it makes it much more unlikely, especially if an alternative diagnosis can be made (e.g. tuberculosis, heart failure). Using conventional cytology diagnosis of malignant mesothelioma is difficult, but immunocytochemistry has greatly enhanced the accuracy of cytology.

Biopsy

Generally, a biopsy is needed to confirm a diagnosis of malignant mesothelioma. A doctor 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.

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 laparoscopy. To obtain tissue for examination, the doctor makes a small incision in the abdomen and inserts a special instrument into the abdominal cavity. If these procedures do not yield enough tissue, more extensive diagnostic surgery may be necessary.

Mesothelioma is staged Ia–IV (one-A to four) based on the TNM status.

The prognosis for malignant mesothelioma remains disappointing, although there have been some modest improvements in prognosis from newer chemotherapies and multimodality treatments.



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