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Benign mesothelioma is a rare but treatable non-cancerous form of mesothelioma. It forms as tumors in the mesothelium, the membrane that lines the thoracic cavity. While a malignant tumor can metastasize or spread to other tissues, benign tumors may grow but do not spread, or metastasize.
Diagnosing benign mesothelioma is similar to malignant tumors. However, it usually requires a biopsy for a doctor to determine if cells benign, not malignant. Treatment is straightforward, usually involving surgery to remove the tumor. Generally, the prognosis for this condition is very good.
Malignant vs. Benign Mesothelioma
The main difference between these types of tumors is that malignant mesothelioma has the potential to spread to other tissues. In contrast, a benign tumor does not. Mesothelioma is rare as a type of cancer, but benign tumors of the mesothelium are even rarer. Also, malignant mesothelioma is strongly connected to asbestos exposure, while the benign form has unknown causes.
There are several subtypes of each kind of mesothelioma. Benign tumors can come in different forms, including benign tumors of the pleura, benign multicystic peritoneal mesothelioma, and papillary mesothelioma. Of these, benign tumors in the pleura are most common. The peritoneal form is rare, with only about 150 cases ever reported, and papillary mesothelioma has only been reported approximately 60 times.
Benign Fibrous Pleural Mesothelioma
The most common of these rare benign mesotheliomas forms in the pleura, or the lining of the lungs. In 2004, approximately 500 cases of benign mesothelioma in the pleura were reported. Most of these tumors first grow in the visceral layer of the pleura, the inner layer surrounding the lungs. Benign pleural tumors can range from small to large, are typically smooth, may have fluid-filled cysts, and are often partially calcified. Tumor cells may be fibrous, cellular, mixed, or a combination of fibrous and cellular.
Benign Multicystic Peritoneal Mesothelioma
Even less common is the type of benign mesothelioma that originates in the peritoneum, the epithelium that lines abdominal organs. This type is most common in women of reproductive age although it can occur in both sexes and at any age. Benign peritoneal mesothelioma is usually multicystic, meaning they contain multiple, fluid-filled cysts. Based on the reported cases, the prognosis of benign peritoneal mesothelioma is very good. Only one death has been reported 12 years after the diagnosis of his disease due to refusal of surgical intervention.
Well-Differentiated Papillary Mesothelioma
Very few cases of well-differentiated papillary mesothelioma (WDPM) have been diagnosed and reported. They are mostly benign tumors, although some also have malignant cells. They are more common in women between the ages of 30 and 40 and are most likely to arise in the peritoneum. In a few cases, these tumors have developed in the pericardium, the lining around the heart. Papillary mesothelioma tumors are characterized by papillary structures, which can only be seen under the microscope. The optimal treatment for WDPMP is not clear due to rare incidence rates. Long-term follow-ups are needed to characterize this type of cancer.
Adenomatoid tumors are often seen in the testis or uterus. These tumors are often classified as benign mesotheliomas because they originate in the mesothelium that surrounds the glands. This type of tumor can become malignant. However, they are most often benign and can be found in the pleura or peritoneum as well as in the testis and uterus.
Although benign tumors are noncancerous and do not spread to other tissues, they can create problems as they increase in size. Benign pleural tumors, for instance, can cause some of the same symptoms as malignant pleural mesothelioma. These symptoms include tightness in the chest, shortness of breath, chest pains, and pleural effusion (the buildup of fluid between the two layers of the pleura). If the tumor is a significant size, it can ultimately cause more serious complications including seizures and coma.
Benign mesothelial tumors of the peritoneum or pericardium may cause similar complications. Complications usually occur when the tumor has grown large enough to cause fluid buildup, resulting in pain or discomfort. In many cases of peritoneal or pericardial benign tumors, there are no symptoms. The tumor may be found coincidentally if the patient is being screened for something else.
Diagnosis for benign mesotheliomas may be accidental if no symptoms are apparent. However, in some cases the tumor grows large enough to cause discomfort. Diagnosis begins with a physical exam and continues with imaging scans. These scans may indicate an unusual mass or lesion, which is expected to be a tumor.
The next step is to determine whether mass is a benign or malignant tumor, whether it is a mesothelioma, and what cell types are involved. A pathologist can examine the biopsied tumor sample under a microscope to determine if the cells are benign. He or she can also determine if the biopsied tissue is of a papillary or adenomatoid type.
This histological approach is not always accurate, but immunohistochemical staining can improve that accuracy. This technique uses antibodies to target specific antigens in tumor cells. It can rule out or find cancerous cells with good accuracy.
If there are no symptoms and a benign mesothelial tumor is small, it may not require treatment. If mor is increasing in size and causing discomfort, the typical treatment is surgery to remove the mass. Treatments are straightforward surgeries with modest recovery periods. In some cases of benign pleural mesothelioma, a segment of a lung or an entire lobe may need to be removed. This will require more recovery time, and increases the possibility of complications.
The prognosis for benign mesotheliomas is overwhelmingly positive, but, as with surgery, there are risks. However, surgical removal of one of these tumors is completely curative. Some patients may experience a recurrence, but recurrence is typically benign and occurs years later. Survival rates of benign mesothelioma are near 100 percent.
Page Medically Reviewed and Edited by Pinar Kanlikilicer, PhD
Dr. Pinar Kanlikilicer has a PhD in Biomedical Engineering. She completed her 5-years of postdoctoral training in the Department of Experimental Therapeutics at MD Anderson Cancer Center. She is currently working in the field of cancer as a research scientist.