Mesothelioma

Generality

Mesothelioma is the medical term for a malignant tumor originating in a cell of the mesothelium.

The mesothelium is the serous membrane that covers the lungs, the heart, some abdominal organs, the testicles in men, the uterus in women and the cavities in which the organs just mentioned reside.

CT scan of a patient with pleural mesothelioma. Note the tumor mass indicated by the yellow arrows compressing the right lung. From wikipedia.org

There are various types of mesothelioma; the best known and most common types are pleural mesothelioma and peritoneal mesothelioma.
The main cause of any mesothelioma in humans is exposure to asbestos or asbestos. Asbestos is a set of minerals that can be easily diffused into the air and are inhaled.
Symptoms of mesothelioma depend on the site of origin of the malignant tumor.
For an accurate diagnosis, biopsy is essential.
Possible treatments include surgery, radiotherapy and chemotherapy.

What is Mesothelioma?

A mesothelioma is any malignant tumor (or cancer) that originates from the cells of the mesothelium.
The mesothelium is a layer of squamous cells, which lines several internal organs (including lungs, heart, some abdominal organs, testicles in men and uterus in women) and the cavities within which these organs reside.
In particular:

• The mesothelium of the lungs and the cavities that contain them are called visceral pleura and parietal pleura, respectively.
  The generic term for pleura includes both visceral and parietal pleura.
• The mesothelium of the heart and the sac that contains it is known as the visceral pericardium (epicardium) and the parietal pericardium, respectively.
  The generic term for pericardium includes both visceral pericardium and parietal pericardium.
• The mesothelium that covers some abdominal organs and the cavity that contains these organs is called, respectively, visceral peritoneum and parietal peritoneum.
  The generic term for peritoneum includes both the visceral peritoneum and the parietal peritoneum.
• The mesothelium of the testicles is known as the vaginal cavity of the testicle.
• The mesothelium of the uterus is known as the perimetry (or serous tunic of the uterus).

The layer of squamous cells forming the different mesotheliums of the human body gives rise to serous-type membranes.

TYPES OF MESOTHELIOMA

There are various types of mesothelioma. The distinction into different types depends on the mesothelium in which the tumor originates.
The best known and most common types of mesothelioma are:

• Pleural mesothelioma: it is mesothelioma that originates at the level of the pleura. Data in hand, it represents, by far, the most common type of mesothelioma in the human being.
  It has good infiltrating abilities (it is capable of spreading to neighboring tissues) and can contaminate the nearby pericardium, with its cancer cells.
• The peritoneal mesothelium: it is the mesothelioma that arises at the level of the peritoneum. It represents another good part of the mesotheliomas that can affect the human being, even if it is decidedly less consistent than pleural mesothelioma.
  It has poor infiltrating capabilities, so it rarely invades adjacent tissues with its cancer cells.

The lesser known and even less common types of mesothelioma are:

• Pericardial mesothelioma: is the mesothelioma that originates from the pericardium, ie the mesothelium within which the cuorei resides.
• Testicular mesothelioma (or mesothelioma of the vaginal tunic of the testicle): is the mesothelioma that originates from the mesothelium of the testicles (also known as the vaginal tunic of the testicle).
• Perimeter mesothelioma (or mesothelioma of the uterine serous tunic): it is the mesothelioma that originates from the mesothelium of the uterus, also known as uterine serous tunic.

A few more details on the pleura and peritoneum

The pleura serves, first of all, to protect the lungs.
Secondly, it produces a lubricating fluid that favors its flow on the surface of the lungs, so as to allow the latter greater freedom of expansion. Between the visceral pleura and the parietal pleura, there is a virtual space known as the pleural space or pleural cavity.
The peritoneum serves to protect and keep the abdominal organs it covers in place. Like the pleura, it produces a lubricating liquid which, interposing itself between the various abdominal organs, promotes mutual sliding.

Causes

For humans, the main cause of mesothelioma is exposure to asbestos or asbestos.
Asbestos is a set of minerals (inosilicates and phyllosilicates), arranged in elongated bodies (the so-called "asbestos fibers") and capable of being easily dispersed in the air (this involves their inhalation).
In order for the readers to realize the "influence of asbestos on the development of mesothelioma, the following statistic is reported, relative to the United Kingdom: 9 out of 10 men with mesothelioma and about 8 out of 10 women with mesothelioma are people who have had contact with asbestos in their life.
The effects of "exposure to" asbestos appear after many years: a mesothelioma can arise after 20, if not 50 years.

Asbestos enters the human organism through the respiratory tract. It is for this reason that the most prevalent mesothelioma is pleural mesothelioma.

RISK FACTORS RELATED TO "ASBESTOS

Asbestos

While once it was widely used in industrial plants for its resistance to fire, acids, microorganisms and wear, today asbestos is no longer in use and many countries around the world have even banned its marketing, precisely because its harmful effects on human health. This greatly reduced the risk of exposure to asbestos and, clearly, also the risk of developing mesothelioma and other related disorders (asbestosis, etc.).

At present, the people still dangerously exposed to asbestos are: those who live in the vicinity of old mining quarries for asbestos, those who live near old buildings with parts in asbestos and those who live near rich natural places. of those mineral components forming the asbestos.
It is important to emphasize this concept: the earlier it begins and the greater the "exposure" to asbestos during the life of an individual, the higher the risk of developing mesothelioma.

• The cement-based tools that produced Eternit (Eternit was the trade name of "asbestos).
• The textile industries that produced sheets, overalls and gloves based on asbestos and derivatives.
• Shipyards and railways.
• Building installations.
• Industries for friction materials, such as brakes and clutches.
• Quarries for the extraction of the minerals that make up asbestos.

OTHER CAUSES OR RISK FACTORS ONLY

By studying the effects of asbestos on humans, some research groups have noted that coming into contact with the SV40 virus in subjects previously exposed to asbestos contributes to the onset of mesothelioma. Scientific findings in this regard are still scarce and require further investigation.
According to other researchers, there are other possible causes or risk factors of mesothelioma: exposure to radiation from radiotherapy, exposure to thorium dioxide and exposure to a mineral known as erionite, present in Turkey.

EPIDEMIOLOGY

In general, mesothelioma is a rather rare malignant tumor. For example, in the UK, it affects 2,600 people every year; in Italy, just over 2,000 individuals per year.
In the past, some studies had highlighted the existence of a higher incidence of mesothelioma in the male population (NB: the ratio with the female population was 5 to 1). Most likely, this trend was linked to the fact that asbestos workers - when this substance was still widely in use - they were mostly men. It would not be surprising if such research, carried out today, provided slightly different data and with a smaller gap between men and women.
Most people with mesothelioma are over 50 years old (patients aged 70 are, by far, the most numerous). This particular incidence in the elderly population is explained by the very slow effects that exposure to asbestos has on humans.

• Pleural mesothelioma accounts for nearly 75% of human mesotheliomas. Thus, about 3 out of 4 mesotheliomas are pleural mesotheliomas.
• Peritoneal mesothelioma accounts for nearly 25% of human mesotheliomas. Therefore, approximately one in 4 mesothelioma is peritoneal mesothelioma.
• Pericardial mesothelioma and mesotheliomas of the internal reproductive organs of men and women account for the remaining percentage. They are very rare.

Symptoms and Complications

Premise: Since pleural mesothelioma and peritoneal mesothelioma are the two most common types of mesothelioma, this chapter will mainly deal with the symptoms of these two malignant tumors of the mesothelium.
Typical symptoms and signs of a pleural mesothelioma are:

• Pain in the chest and sometimes in the lower back
• Shortness of breath (dyspnoea)
• Persistent cough and / or hoarseness
• Pleural effusion
• Hemoptysis (coughing up blood)
• Fever above 38 ° C, with sweating, especially at night
• Muscle fatigue and weakness
• Difficulty swallowing
• Unexplained weight loss

Typical symptoms and signs of peritoneal mesothelioma are:

• Abdominal pain
• Abdominal swelling, due to a buildup of fluid (ascites)
• Sense of nausea and recurrent vomiting
• Loss of appetite
• Unexplained decrease in body weight
• Diarrhea or constipation
• Presence of an abdominal mass, recognizable to the touch

SPECIAL FEATURES OF THE INITIAL STAGES

Very often, at the beginning, both pleural and peritoneal mesothelioma are asymptomatic, that is, without obvious symptoms and signs.
This particularity makes early diagnosis difficult.

COMPLICATIONS OF THE PLEURIC MESOTHELIOMA

In severe cases, pleural mesothelioma can cause the appearance of several tumors in the thoracic area, the collapse of one or both lungs (pneumothorax) and pulmonary embolism.
Furthermore, it is a malignant tumor with metastasizing capacity, so it can spread its tumor cells in organs and tissues distant from the site of origin (NB: the cells that a malignant tumor disperses in organs and tissues distant from the site of origin are named of metastases).

COMPLICATIONS OF THE PERITONEAL MESOTHELIOMA

In the most severe cases, peritoneal mesothelioma is responsible for:

• Blood clots inside the venous vessels (thrombophlebitis)
• Jaundice
• Hypoglycemia
• A further worsening of the ascites
• Metastasis, although it should be noted that its metastatic power is lower than that of pleural mesothelioma

SYMPTOMS OF PERICARDIAL MESOTHELIOMA

Mesothelioma affecting the pericardium can cause the appearance of: pericarditis, heart failure, pulmonary embolism, cardiac tamponade, chest pain, orthopnea and cough.

Diagnosis

Generally, the diagnostic process that leads to the identification of a mesothelioma begins with a thorough physical examination and a careful medical history (clinical history). Then, it continues with some diagnostic imaging tests, including X-rays, CT, resonance nuclear magnetic and PET.

Finally, it ends with a biopsy, the most indicative examination and the one that confirms any suspicion born during the previous evaluations.

IMPORTANCE OF THE HISTORY

As mentioned, mesothelioma almost exclusively affects people exposed to asbestos.
This characteristic makes the medical history a fundamental point of the diagnostic process, as an individual who has never had contact with asbestos in life, even if he has suspected symptoms, most likely suffers from a disorder other than mesothelioma.
In this regard, it should be noted that the clinical manifestations of mesotheliomas closely resemble those of other morbid conditions. To cite one example, a pleural mesothelioma has symptoms and signs that mimic the symptoms and signs of lung cancer or pulmonary fibrosis.

IMAGE DIAGNOSTICS

The diagnostic imaging tests allow the doctor to identify the exact location of the tumor mass or masses and to see if they have invaded other organs or tissues, or if they have had particular effects (pleural effusion, ascites, etc.).

BIOPSY

The biopsy consists in the collection of a sample of cells from the tumor mass and in the laboratory analysis of this sample.
Through the analysis of tumor cells, the doctor is able to understand the type of cell that gave rise to the malignant tumor: if it appears that the process of formation of the tumor mass began at the level of a mesothelial cell (ie a mesothelium), then the aforementioned tumor mass is a mesothelioma.
In addition, biopsy is useful because it allows two important characteristics of a malignant tumor to be detected: staging and grade.
In the case of pleural mesothelioma, the collection of the cell sample for biopsy is done through thoracoscopy or thoracotomy procedures.
In the case of peritoneal mesothelioma, the sample of cells for biopsy is taken by means of a laparoscopy.

What are the staging and grade of a malignant tumor?
The staging of a malignant tumor includes all the information, collected during the biopsy, concerning the size of the tumor mass, its infiltrating power and its metastasizing capacity.
The degree of a malignant tumor, on the other hand, includes all those data, which emerged during the biopsy, concerning the extent of transformation of the malignant tumor cells, compared to their healthy counterparts.

Treatment

The choice of which treatment to adopt in case of mesothelioma depends on several factors, including: the stage and grade of the malignant tumor (presence of metastases, progression of the disease, etc.), the general state of health of the patient (patients are generally elderly people with other ailments) and the affected body regions.
Currently, the treatment options for mesothelioma are: surgery, radiotherapy and chemotherapy.

SURGERY

The goal of surgery is to remove the tumor that makes up mesothelioma. For less severe mesotheliomas, surgical removal can also provide good results. However, in general, mesotheliomas lend themselves little to resection (ie elimination by surgery).
To further complicate matters, then, may be the uncomfortable location of the malignant tumor: if the latter, in fact, originates in an area that is difficult to reach with surgical instruments, the removal operation is even more complex.

RADIOTHERAPY

In the case of mesothelioma, radiotherapy can represent an "alternative to" surgery - if this is not practicable - or a form of adjuvant treatment, to be performed after surgical removal of the tumor mass (adjuvant radiotherapy).
When radiotherapy is of adjuvant value, it destroys cancer cells that the surgeon has not been able to remove.

CHEMOTHERAPY

Chemotherapy consists in the administration of one or more anticancer drugs, systemically, intrapleurally (ie directly in the thoracic cavity) or intraperitoneally (ie directly in the abdominal cavity).
Depending on the characteristics of the mesothelioma present, the treating physician can decide whether to opt for pre-surgical chemotherapy (also called neoadjuvant chemotherapy) or for post-surgical chemotherapy (also known as adjuvant chemotherapy).
The goal of neoadjuvant chemotherapy is to reduce the tumor mass, so as to make subsequent surgical removal easier.
The goal of adjuvant chemotherapy, on the other hand, is to eliminate the tumor cells that the surgeon, through resection, was unable to remove.

POSSIBLE CARE OF THE FUTURE

Recently, doctors and researchers are experimenting with the effects of some particular medicines, belonging to the category of monoclonal antibodies and also known as biological drugs.
Among the biological drugs that appear to have therapeutic effects against mesothelioma, tremelimumab deserves a particular mention.

Prognosis

Mesothelioma almost always has a negative prognosis, as its diagnosis occurs, very often, too late, when the situation is already strongly compromised.
The average survival rate for pleural or peritoneal mesothelioma is 12 months. However, it should be noted that some patients manage to survive even 3 years (obviously with the most appropriate therapies).
The average survival rate for pericardial mesothelioma is 10 months.