Malignant Mesothelioma

Malignant mesothelioma is a rare type of cancer that forms on the mesothelium, a protective tissue that lines several of the body’s internal organs. Exposure to asbestos is almost exclusively responsible for the development of malignant mesothelioma.
The prevalence of lung cancer among asbestos-exposed workers has been documented since the 1920s. The first case report of malignant mesothelioma, derived from records at Massachusetts General Hospital, was published in 1947. It was not until 1999, however, that the U.S. government began tracking malignant mesothelioma as a recognized cause of death.

Malignant mesothelioma can develop in four parts of the body:

Pleural Mesothelioma

The most frequently affected site is the pleura, or the mesothelial lining that surrounds the lungs. Cancer that originates here is classified as pleural mesothelioma.

Pericardial Mesothelioma

Another variation of the disease, pericardial mesothelioma, develops in the protective sac surrounding the heart.

Peritoneal Mesothelioma

The second most common location for the tumors to originate is the abdomen. Asbestos cancer that develops here is known as peritoneal mesothelioma.

Testicular Mesothelioma

The rarest location for mesothelioma to be found is in the lining of the testicles, known as the tunica vaginalis. iThis form of the cancer is medically classified as testicular mesothelioma.

While most diagnosed cases of mesothelioma are malignant, doctors sometimes find mesothelioma tumors that are non-cancerous.

Benign vs. Malignant Mesothelioma

As with most forms of cancer, mesothelioma can be classified as either malignant or benign. Benign tumors can be surgically removed because they are non-cancerous and incapable of spreading throughout the body. Malignant mesothelioma, on the other hand, is cancerous, highly aggressive and more challenging to treat. While asbestos has been definitively linked to causing malignant mesothelioma, benign mesotheliomas often result from other disorders such as infectious pleuritis, hepatic cirrhosis or systemic lupus erythematosus.
Because a mesothelioma patient may present with benign and malignant tumors simultaneously, a doctor must be able to differentiate between the two before recommending a course of treatment. Benign tumors do not metastasize, so if a tumor spreads to local glands, cells and connective tissue it is considered malignant.
A doctor can also determine a tumor’s potential malignancy based on how deeply it penetrates into the pleura. Benign tumor cells typically conglomerate at a relatively shallow depth, while malignant cells can reach the fat or muscle areas of the chest wall or well into the patient’s lung tissue.
Total cell enlargement, as opposed to just the enlargement of the cell’s nucleus, is another indicator of malignancy. Large aggregations of cells with irregular nuclei and hyperchromasia (an elevated level of the DNA protein chromatin) almost always imply a malignant diagnosis. Benign lesions feature linear cells that typically lack papillae, which are dome-shaped structures found on the cell surface.

Malignant Mesothelioma Cell Types

A malignant mesothelioma tumor may be made up of three different cell types:

Epithelial cells appear the most frequently in malignant mesothelioma tumors, and this subtype accounts for between 50 and 70 percent of all cases. These cells, which are uniform and sharply defined, feature prominent nuclei and often form complex branching patterns.

These spindle-shaped Sarcomatoid cells typically lack strong characteristics, occurring in approximately 10 to 20 percent of reported malignant mesothelioma cases.

Malignant mesothelioma is considered biphasic when both epithelial and sarcomatoid cells are present and each type accounts for at least 10 percent of the tumor’s mass. Biphasic (mixed) cells are present in 20 to 35 percent of all malignant mesotheliomas.

Doctors use these histological classifications to develop a prognosis and treatment plan for malignant mesothelioma patients. Although the life span associated with malignant mesothelioma can be short, your cell type can account for differences in life expectancy ranging up to 200 days.
Of all subtypes, mesotheliomas involving epithelial cells are typically most responsive to treatment, which often leads to a better prognosis. Because sarcomatoid cells are the most resistant to treatment, some surgeons do not consider sarcomatoid tumors eligible for resection. Biphasic cells are also considered less responsive to treatment than epithelial.
Diagnosing a patient’s specific type of malignant mesothelioma can be challenging for doctors. One common obstacle is differentiating mesothelioma from adenocarcinoma, the most common form of lung cancer among non-smokers.

Mesothelioma Guide

The type of mesothelioma diagnosed and its location in the body are extremely important factors when choosing a doctor. Our free guide includes an up to date list of every specialist across the country – get yours sent right away.