Malignant Mesothelioma

Malignant Mesothelioma

By Elizabeth Morgan

Malignant mesothelioma is a rare cancer in which malignant or cancerous cells form in the thin layers of tissue lining the human chest, heart or abdomen. When the cancer is in the chest, it affects the pleura or tissue lining the lungs and is called malignant pleural mesothelioma. In the abdomen, a cancer of the peritoneum or tissue lining the abdominal cavity and covering various organs is called malignant peritoneal mesothelioma. Avoiding exposure to asbestos can largely prevent malignant mesotheliomas.

If a detailed medical history and physical exam suggests malignant mesothelioma as a possible diagnosis, a variety of diagnostic tests may be performed, including blood tests, x-rays, MRIs, CT scans and biopsies. Malignant mesotheliomas are graded upon the extent they have spread. A stage I, or localized, malignant mesothelioma is one that has not spread beyond the area it originated in. Stage II, III and IV malignant mesotheliomas are advanced, and may have spread to lymph nodes or to surrounding or distant organs and tissues. Some cancer treatment centers are involved in clinical trials using biotherapy and immunotherapy.

When a patient has symptoms suggesting malignant mesothelioma, a doctor starts with imaging techniques to confirm a diagnosis. Magnetic resonance images (MRI) or positron emission tomography (PET) images are taken to determine the extent of spread of a cancer; PET is most expensive but also the most accurate.

Once cancer is suspected, a tissue biopsy is needed to confirm the diagnosis. If the pleura or tissue lining the chest and lungs is involved, a thoracoscopy is performed, usually under local anesthesia. Tissue and fluid can be collected through this opening. Similarly, if the peritoneum or tissue lining the abdominal cavity and abdominal organs is involved, a peritoneoscope is inserted into the abdominal cavity to collect biopsy tissue. Depending on the cell type, a diagnosis of malignant mesothelioma can be made. Malignant mesotheliomas are of three cell types: epithelioid, mixed and sarcomatoid. In general, epithelioid malignant mesotheliomas are the most common and carry the best prognosis; sarcomatoid ones are the most rare with the shortest survival time.

The next step is to stage the cancer as localized, advanced or recurrent. There are three staging systems in use, each with four stages: the Butchart System, the TNM System and the Brigham System.

Malignant mesotheliomas are highly aggressive cancers, usually linked to asbestos exposure. The American Cancer Society and National Cancer Institute are good resources for information on ongoing clinical trials and enrollment criteria. While radiotherapy is palliative in chest pain and chest wall spread, it has no effect on survival. Photodynamic therapy is being evaluated for earlier stages of malignant pleural mesothelioma; it combines the injection of a drug that makes cancer cells sensitive to light with the use of light of a certain wavelength to kill these cells.

The University of Chicago’s Cancer Research Center is leading a trial that combines the anti-cancer drugs gemcitabine and cisplatin, which kill cancer cells, with the biological agent bevacizumab, which slows the growth of cancerous tissue and blood vessels in this tissue. Researchers at the National Cancer Institute have identified a protein called mesothelin that is present in higher levels in mesothelioma cancer cells than in surrounding normal tissue.