Localized malignant mesothelioma is a rare form of this cancer that forms fewer tumors that are more well-defined than in most cases of mesothelioma, which are referred to as diffuse. Other characteristics are similar, making diagnosis difficult but important. The treatment and prognosis are very different between localized and diffuse mesothelioma.
Localized vs Diffuse Mesothelioma – What’s the Difference?
Most cases of mesothelioma of diagnosed mesothelioma are diffuse, but in rare cases the tumors may be considered localized. There are both similarities and differences between these two types:
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- The vast majority of diagnosed cases of mesothelioma are diffuse, meaning the tumors that form are small, multiple, and spread out over a significant area of tissue, organs, or multiple parts of the body.
- Localized tumors are fewer in number and have well-defined boundaries. They tend to be localized to one area of one organ or part of the body.
- Just 101 cases of localized malignant mesothelioma have been reported in English-language journals.
- Of those cases, 75% were in men and 82% were pleural, statistics similar to those seen in diffuse mesothelioma.
- As with diffuse mesothelioma, most localized cases are epithelioid by cell type with some cases of sarcomatoid and some a mixture of cells, known as biphasic.
- The histological features, or characteristics of the cells, are usually identical between diffuse and localized types.
- Patients diagnosed with localized mesothelioma have a better prognosis than those diagnosed with diffuse mesothelioma.
- Treatment strategies are often different for these two types, with localized mesothelioma usually warranting a more aggressive surgical approach.
Diagnosing and Misdiagnosing Localized Malignant Mesothelioma
The course of diagnosis runs through the same steps for any type of mesothelioma, beginning with a physical exam and routine tests to rule out other causes of symptoms.
If cancer is suspected or another illness cannot be determined, doctors will order imaging scans to look for unusual areas of tissue. They will then do a biopsy to remove tissue from a suspected area of malignancy.
Pathologists look at those cells under a microscope to determine if they are benign or malignant. If they are malignant, they describe the cell type and any characteristics that help make a diagnosis. The features at the cellular level are identical for localized and diffuse mesothelioma, which can lead to confusion.
The larger features of the tumors are significantly different, which helps distinguish between the two. However, because localized mesothelioma is so rare, it may be misdiagnosed as another type of cancer.
For example, in one case study a patient received a diagnosis of a benign localized fibrous tumor that turned out to be localized mesothelioma. She had no previous exposure to asbestos and had no symptoms until months later when typical mesothelioma symptoms began. By then the cancer had grown and she received the correct diagnosis.
Treating Localized Mesothelioma
For most cases of mesothelioma, treatment involves a multi-modal approach, utilizing chemotherapy, surgery, and/or radiation therapy in addition to any emerging treatments that may help, such as immunotherapy.
A major roadblock in treating diffuse mesothelioma is the nature of the tumors. Because they spread out so far, surgery is often not indicated. With localized mesothelioma, however, surgery is more likely to be successful.
In most cases of localized malignant mesothelioma, the patient will undergo an aggressive surgery to remove the tumors. This may be followed or preceded by chemotherapy or radiation as necessary. Doctors often recommend aggressive treatment because it may be curable for localized tumors.
What is the Prognosis for Localized Malignant Mesothelioma?
The prognosis for localized mesothelioma is generally much better than for diffuse mesothelioma. The more common, diffuse form of this cancer has a poor prognosis because the small, multiple, and diffuse tumors are difficult to manage or remove completely with surgery.
In the localized form, an individual has one or two tumors with clear, defined boundaries. Localized tumors are easier to remove with surgery, resulting in a better prognosis and a longer life expectancy. However, because localized mesothelioma is rare and studies of it limited, accurate estimations of survival times or prognosis are limited.
One study reviewed the literature, but found it difficult to come up with a good average or median survival time. Some studies indicated a median survival of 12 to 36 months, while others reported median survival times of up to 29 months.
What was clear from these studies was that survival time is longer and prognosis significantly more positive for a diagnosis of localized as compared to diffuse mesothelioma.
Localized malignant mesothelioma is rare, but it does occur, both with and without known asbestos exposure. How it will progress is not always certain, but patients with this type of mesothelioma have a better chance of survival after aggressive surgery. Getting an accurate diagnosis as early as possible is essential.