Malignant mesothelioma is one of the most common types of primary tumors of the pleura (the thin membrane lining the lungs). Malignant mesothelioma is classified into three: biphasic, epithelioid and sarcomatoid. Sarcomatoid mesothelioma accounts for between 7 and 20 percent of all mesothelioma cases. Sarcomatoid is the most aggressive, fast grower(metastasize) and harder to treat.
There are 3 types of sarcomatoid mesothelioma consisting of varying cell structures and characteristics:
1. Transitional mesothelioma – has plump and spindle-shaped cells.
2. Lymphohistiocytoid mesothelioma – has large, spindle-shaped cells with inflammatory cells throughout. It accounts for less than 1% of all cases.
3. Desmoplastic mesothelioma – it generally lacks a distinct pattern hence the most difficult to diagnose.
It consists of collagen bundles and elongated cells and accounts for about 5% of all cases. Sarcomatoid cell type is associated with asbestos exposure. Asbestos is a naturally occurring fibrous salt that was used in the manufacturing industry for many years. Asbestos fibers cause inflammation of the pleura which develops into tumour cells. Sarcomatoid tumours present as small nodules scattered on the surface of the lung lining which may grow and merge to form a sheet-like tumour spread across the pleura. A tumour may appear with or without effusion and can also be found along the peritoneum.
Symptoms related to sarcomatoid mesothelioma are generally like those of other types of mesothelioma. The following list comprises of the general symptoms of sarcomatoid mesothelioma:
- Shortness of breath
- Weight loss
- Coughing up blood
- Abdominal fullness
Symptoms of the sarcomatoid of the pleura are distinct from those of the peritoneum. Those of the pleura include weight loss, fatigue, shortness of breath and difficulty in breathing while those of the peritoneum include loss of appetite, nausea, pain in the abdomen and swelling.
Diagnosing sarcomatoid mesothelioma is difficult because in most cases, symptoms of the pleural mesothelioma mimic those of other respiratory diseases such as asthma and pneumonia. The first step when carrying out diagnosis is to identify the tumour cells through imaging (X-ray, CT scan or MRI). To determine the specific cell type, a biopsy (tissue sample) from a tumour is taken for close examination by the physician.
Tissue staining technique can then differentiate between sarcomatoid mesothelioma from other types of cancers. In this technique, antibodies are used to identify specific proteins in the tissue hence confirming the cell types. The reaction is clearly visible under a microscope. Making a definitive diagnosis of the three types of sarcomatoid mesothelioma is very difficult. Treatments and prognosis Due to the aggressiveness of this type of tumours, the prognosis is mostly very poor and there are not many treatment options. Conventional treatment includes chemotherapy, surgery or radiation therapy.
Sarcomatoid tumours are hard to treat because in most cases patients are diagnosed when the tumour cells have already metastasized to different body parts. In particular, treating pleural mesothelioma through surgery is hard as tumours typically penetrate the chest wall hence very complicated to remove. In peritoneal mesothelioma, the tumour attaches around the intestines also making it very difficult to remove. Until recently, chemotherapy was not successful in treating sarcomatoid tumours.
However, a new drug called doxorubicin has shown good effectiveness especially when combined with sodium selenite. This treatment option is still undergoing trial. The current treatment involves a combination of doxorubicin with other cancer drugs but the response rate is very low. The other drugs are cyclophosphamide, dacarbazine, and vincristine.