What are the other Names for this Condition? (Also known as/Synonyms)

• Malignant Mesothelioma In Situ

What is Mesothelioma In Situ? (Definition/Background Information)

• A malignant mesothelioma is a malignancy of the mesothelial cells (membrane lining the various body cavities). They are known to mostly arise in the pleura and peritoneum, and rarely, in the pericardium, the tunica vaginalis of testis, and ovary
• Based on the cell type or histology, the tumor is classified into the following types:
  • Malignant epithelial mesothelioma
  • Malignant sarcomatoid mesothelioma
  • Malignant biphasic mesothelioma
• Mesothelioma In Situ represents an early stage of malignant mesothelioma. The tumor is diagnosed under a microscope, on examination of the cancer cells by a pathologist. The tumor is confined to the mesothelial layer and the cells of the tumor markedly exhibit atypical features
• Mesothelioma In Situ may be associated with asbestos exposure (inhalation or swallowing of asbestos dust or fibers), certain surgical procedures, and radiation treatment to cancers in the chest or abdominal region. The cause of formation of the tumor is not well-established
• Mesothelioma In Situ is considered as a stage 0 (pre-cancer stage) of malignant mesothelioma. The tumor can be found in the pleura, pericardium, peritoneum, or other sites. The signs and symptoms depend upon the location of the tumor
• Small-sized tumors during the initial stages may remain asymptomatic. Large-sized tumors can cause pain, obstructive symptoms, fatigue, and weight loss. However, no invasion of the surrounding tissue or metastasis is noted
• The treatment of Mesothelioma In Situ is undertaken through a surgery. The prognosis is generally excellent with complete surgical excision and removal of the tumor

Who gets Mesothelioma In Situ? (Age and Sex Distribution)

• Mesothelioma In Situ may occur in children and young adults; however, a majority are found in older adults
• Both males and females are affected, although males are at a higher risk by virtue of their occupation
• No racial or ethnic group preference is generally noted

What are the Risk Factors for Mesothelioma In Situ? (Predisposing Factors)

Currently, no definitive risk factors are noted for the development of Mesothelioma In Situ. But it may be associated with the following factors:

• Association with asbestos/fiberglass exposure is strongly noted; the tumors may often develop many years after exposure to these substances. Workers exposed to asbestos include the following and those involved in occupations such as:
  • Manufacturing of industrial products containing asbestos such as paints, insulation, floor tiles, ceiling, etc.
  • Construction workers, home builders
  • Electricians
  • Firefighters
  • Demolition workers
  • Military personnel
  • Those working in chemical plant manufacturing facilities, refineries, power plants, etc.
  • Shipyard workers
• Secondary asbestos exposure (inhalation) during the job, when one may be exposed being in the vicinity. The environmental asbestos exposure can occur in a variety of ways
• Iatrogenic tumors: Some tumors have been reported to form following medical treatment for angina pectoris; for tumors affecting the pericardium
• Chronic smoking
• Radiation therapy for a variety of cancers: In rare cases, treatment for breast or abdominal cancer using radiation therapy is also known to cause the formation of malignant mesothelioma
• Exposure to eronite, a type of naturally-occurring mineral fiber, in some parts of the world (e.g. Turkey)
• Family history of mesothelioma: Mutations in BAP1 gene that can run in some families can increase the risk for malignant mesothelioma. The gene mutation can also cause an increased risk for a variety of cancers, such as ocular melanoma, clear cell renal cell carcinoma, liver cancer including intrahepatic cholangiocarcinoma, melanoma of skin, etc. in such individuals
• In experimental animal models, simian virus 40 (SV40, which is generally found in monkeys and humans) has been shown to cause malignant mesothelioma. However, whether SV40 causes mesothelioma in humans is not yet definitely established

Note:

• The adverse health effect caused by smoking and exposure to asbestos may act as a combination factor in some individuals and result in a much amplified risk for mesothelioma
• In some cases, no association to any of the above factors may be identified

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Mesothelioma In Situ? (Etiology)

The exact cause and mechanism of formation of Mesothelioma In Situ is unknown. However, the tumor formation seems to be influenced by exposure to certain carcinogenic substances (such as asbestos fibers), radiation therapy for cancer, and medical procedures.

• Mesotheliomas have been shown to have a variety of different genetic mutations
• Long-term exposure to asbestos:
  • Asbestos is a silicate mineral with a fibrous structure. Due to its high heat resistance, it is used as a versatile insulating material in several industries including construction, firefighting, automobile industry, etc. However, it is harmful to humans and is recognized as a hazardous material
  • It is researched that when the asbestos particles get into the body (part/site), they irritate the body tissue causing genetic damage. The entry into the human body may be through inhalation of asbestos dust particles or by inadvertently swallowing small-sized asbestos fibers
  • Generally it takes years to develop mesothelioma; around 10-50 years following exposure to asbestos or asbestos products
• In general, it is known that cancers form when normal, healthy cells begin transforming into abnormal cells - these cancer cells grow and divide uncontrollably (and lose their ability to die), resulting in the formation of a mass or a tumor
• The transformation of normally healthy cells into cancerous cells may be the result of genetic mutations. Mutations allow the cancer cells to grow and multiply uncontrollably to form new cancer cells
• These tumors can invade nearby tissues and adjoining body organs, and even metastasize and spread to other regions of the body

What are the Signs and Symptoms of Mesothelioma In Situ?

The signs and symptoms of Mesothelioma In Situ depend upon the location of the tumor. These may include:

• Mesothelioma In Situ can be observed in the peritoneum (abdomen), pleura (lung), or pericardium (heart). It may rarely affect the testis and ovary
• Low-grade fever and profuse sweating
• Tiredness or fatigue
• Tumors in the pleura or pericardium can lead to:
  • Shortness of breath or rapid breathing
  • Pleural or pericardial effusion; an abnormal collection of fluid within the pleura/pericardium
  • Chest pain or discomfort, such as feelings of heaviness/fullness of the chest
  • Intermittent cough
  • Tumors in the heart or lung can spread and obstruct major blood vessels or airways
• Tumors in the peritoneum can lead to:
  • Abdominal pain; swollen abdomen
  • Nausea and vomiting
  • Ascites; an abnormal collection of fluid within the abdominal cavity
• Fainting or feeling faint, dizziness
• Weight loss

There are no signs and symptoms during the initial stages of tumor growth and development. Also, small-sized tumors usually do not cause any symptoms. But, occasionally they may become painful, if the surrounding structures are compressed.

How is Mesothelioma In Situ Diagnosed?

The following tools may be used towards establishing a diagnosis of Mesothelioma In Situ:

• Complete evaluation of family (medical) history, along with a thorough physical examination
• X-ray of the affected region
• CT or CAT scan with contrast of the affected region may show the presence of a mass. This radiological procedure creates detailed 3-dimensional images of structures inside the body
• MRI scans of the affected region: Magnetic resonance imaging (MRI) uses a magnetic field to create high-quality pictures of certain parts of the body, such as tissues, muscles, nerves, and bones. These high-quality pictures may reveal the presence of the tumor
• Whole-body PET scan, bone scan of affected region to check for tumor metastasis. This helps with the staging of the tumor

Although the above modalities can be used to make an initial diagnosis, a tissue biopsy of the tumor is necessary to make a definitive diagnosis to begin treatment. The tissue for diagnosis can be procured in multiple different ways which include: 

• Fine needle aspiration (FNA) biopsy of the tumor: A FNA biopsy may not be helpful, because one may not be able to visualize the different morphological areas of the tumor. Hence, a FNA biopsy as a diagnostic tool has certain limitations, and an open surgical biopsy is preferred
• Core biopsy of the tumor
• Open biopsy of the tumor

Tissue biopsy of the tumor:

• A biopsy of the tumor is performed and sent to a laboratory for a pathological examination. A pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis. Examination of the biopsy under a microscope by a pathologist is considered to be gold standard in arriving at a conclusive diagnosis
• Biopsy specimens are studied initially using Hematoxylin and Eosin staining. The pathologist then decides on additional studies depending on the clinical situation
• Sometimes, the pathologist may perform additional studies, which may include immunohistochemical stains, electron microscopy, and molecular studies to assist in the diagnosis

Note:

• It is rare to find a tumor that has purely one subtype. Often, there is a mixture of more than one cell type. The predominant pattern determines the histological subtype of the tumor
• Due to the rarity of these tumors, the diagnosis of this malignancy can be missed. It can even cause diagnostic challenges during a frozen section biopsy

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Mesothelioma In Situ?

Complications due to Mesothelioma In Situ are dependent upon the site of the tumor and could include the following:

• Pleural tumors may result in:
  • Large tumors can obstruct the bronchus (airways) and other adjoining organs/structures
  • Severely impaired lung function
• Pericardial tumors may result in:
  • Congestive heart failure, depending on the location of the tumor in the heart
  • Cardiac tamponade due to fluid around the pericardium, which can lead to low blood pressure, fatigue, anxiety, rapid breathing, and fainting
  • Increased risk for thromboembolism (blood clot obstructing a blood vessel) 
• Large tumors can compress adjoining organs and structures and impair their function
• Recurrence of the tumor after surgery, when the entire tumor is not removed
• Blood loss during invasive treatment methods may be heavy
• Damage of vital nerves, blood vessels, and surrounding structures during surgery

Local infiltration into the surrounding tissues or organs, and spread of the tumor to other sites in the body is generally not observed.

How is Mesothelioma In Situ Treated?

Mesothelioma In Situ is a precursor to malignant mesothelioma, and hence, it is represented as a stage 0 tumor. The healthcare provider will determine the best treatment option to be provided. If left untreated, this tumor can become invasive malignant mesothelioma.

The treatment for Mesothelioma In Situ may consist of the following measures:

• Surgery: A complete excision and removal of the tumor is typically undertaken
• Radiation therapy and/or chemotherapy is usually not required
• Immunotherapy: It is a newer method of treatment that has shown promising results in some individuals. The healthcare provider will determine if immunotherapy is to be employed in treating the tumor
• Follow-up care with regular screening and check-ups are important

How can Mesothelioma In Situ be Prevented?

Current medical research has not established a method of preventing the formation of Mesothelioma In Situ. However, the following factors may be considered to reduce the risk of cancer development:

• Avoid or stop smoking: Individuals, who are smokers or have a prior history of the condition or suffer from other lung diseases, should regularly follow-up with their primary care physician to ensure that their lung functions are normal
• Reducing exposure to known causative agents such as asbestos and asbestos products 
• Early detection of exposure to asbestos dust particles can help avoid further exposure
• Wearing appropriate respirators and masks while performing jobs that involve dust, chemicals, and metals
• While working in industry, maintain a clean work area that is dust-free. Also, regularly shower and change clothes after industrial work
• Ensure that industrial safety regulations for exposure to hazardous materials is adhered to at workplaces
• Ensure that the industries strictly comply with implementation of prevalent statutory codes on occupational safety measures, especially with respect to workplace exposure
• Undertake routine screening of individuals working in environment where exposure to asbestos is evident
• Government regulations have decreased or even eliminated the use of asbestos through increased safety measures and through the usage of substitute products (instead of asbestos)
• It is recommended that regular screening be undertaken for mesothelioma, if any of the following tumors are observed:
  • Clear cell renal cell carcinoma
  • Intrahepatic cholangiocarcinoma (a type of liver cancer)
  • Cutaneous melanoma
  • Uveal or ocular melanoma

Due to its high metastasizing potential and recurrence rate, regular medical screening at periodic intervals with blood tests, scans, and physical examinations, are mandatory for those who have already been treated for this tumor.

What is the Prognosis of Mesothelioma In Situ? (Outcomes/Resolutions)

• The prognosis of Mesothelioma In Situ is generally excellent with (early) adequate treatment (complete surgical removal of the tumor) and long-term follow-up and regular screening for cancer
• If the tumor is left untreated or if there is a delay in treatment, Mesothelioma In Situ can develop into malignant mesothelioma, which is an invasive/aggressive form of malignancy. In such cases, the prognosis is guarded-to-poor

Additional and Relevant Useful Information for Mesothelioma In Situ:

Malignant epithelial mesothelioma is the most common histological type of malignant mesothelioma. It can occur in all 5 body sites, though the most frequent location is the pleura (in the lungs).