Bíltúr
Ég vissi ekki fyrr en í fyrradag að djörkí væri til sölu á Íslandi. Já og sjóarabitar. Svo komst ég á snoðir um tilvist víkingaskákar. Ég fór semsagt, ásamt frænda mínum, í bíltúr vestur á firði.
,,Ertu viss um að þið viljið fara yfir heiðina á þessum bíl?" Var ég spurður þegar ljóst var hversu hæpið yrði að Pelinn myndi rúlla upp Hrafnseyrarheiðinni, svona á ,,heilsársdekkjunum" og fyrsta kuldaskot þessa veturs orðið staðreynd. ,,Maðurinn þarf að sjá Dynjanda", svaraði ég af bragði og það var nóg. Málið var útrætt og allir í herberginu áttuðu sig um leið á alvöru málsins:
,,Ertu viss um að þið viljið fara yfir heiðina á þessum bíl?" Var ég spurður þegar ljóst var hversu hæpið yrði að Pelinn myndi rúlla upp Hrafnseyrarheiðinni, svona á ,,heilsársdekkjunum" og fyrsta kuldaskot þessa veturs orðið staðreynd. ,,Maðurinn þarf að sjá Dynjanda", svaraði ég af bragði og það var nóg. Málið var útrætt og allir í herberginu áttuðu sig um leið á alvöru málsins:
1 Comments:
At 06 March, 2009 04:03,
Anonymous said…
Asbestos
Mesothelioma is a form of
cancer that is almost always caused by previous exposure to Asbestos.
In this disease, malignant cells develop in the mesothelium, a
protective lining that covers most of the body's internal organs. Its
most common site is the pleura (outer lining of the lungs and internal
chest wall), but it may also occur in the peritoneum (the lining of
the abdominal cavity), the heart, the pericardium (a sac that
surrounds the heart) or tunica vaginalis.
Most people who develop Mesothelioma have worked on
jobs where they inhaled Asbestos particles, or they
have been exposed
to Asbestos dust and
fiber in other ways. Washing the clothes of a
family member who worked with asbestos can also put a person at risk
for developing mesothelioma. Unlike lung cancer, there is no
association between Mesothelioma and smoking.
Compensation via Asbestos
funds or lawsuits is an important issue in
mesothelioma (see Asbestos and the law).
The symptoms of Mesothelioma include
shortness of breath due to pleural effusion (fluid between the lung
and the chest wall) or chest wall pain, and general symptoms such as
weight loss. The diagnosis may be suspected with chest X-ray and CT
scan, and is confirmed with a biopsy (tissue sample) and microscopic
examination. A thoracoscopy (inserting a tube with a camera into the
chest) can be used to take biopsies. It allows the introduction of
substances such as talc to obliterate the pleural space (called
pleurodesis), which prevents more fluid from accumulating and pressing
on the lung. Despite treatment with chemotherapy, radiation therapy or
sometimes surgery, the disease carries a poor prognosis. Research
about screening tests for the early detection of mesothelioma is
ongoing.
Symptoms of Mesothelioma
may not appear until 20 to 50 years after exposure to Asbestos.
Shortness of breath, cough, and pain in the chest due to an
accumulation of fluid in the pleural space are often symptoms of
pleuralMesothelioma
Symptoms of peritoneal Mesothelioma include weight
loss and cachexia, abdominal swelling and pain due to ascites (a
buildup of fluid in the abdominal cavity). Other symptoms of
peritoneal Mesothelioma
may include bowel obstruction, blood clotting abnormalities, anemia,
and fever. If the cancer has spread beyond the mesothelium to other
parts of the body, symptoms may include pain, trouble swallowing, or
swelling of the neck or face.
These symptoms may be caused by Mesothelioma or by other,
less serious conditions.
Mesothelioma that affects
the pleura can cause these signs and symptoms:
chest wall pain
pleural effusion, or fluid surrounding the lung
shortness of breath
fatigue or anemia
wheezing, hoarseness, or cough
blood in the sputum (fluid) coughed up (hemoptysis)
In severe cases, the person may have many tumor masses. The individual
may develop a pneumothorax, or collapse of the lung. The disease may
metastasize, or spread, to other parts of the body.
Tumors that affect the abdominal cavity often do not cause symptoms
until they are at a late stage. Symptoms include:
abdominal pain
ascites, or an abnormal buildup of fluid in the abdomen
a mass in the abdomen
problems with bowel function
weight loss
In severe cases of the disease, the following signs and symptoms may be present:
blood clots in the veins, which may cause thrombophlebitis
disseminated intravascular coagulation, a disorder causing severe
bleeding in many body organs
jaundice, or yellowing of the eyes and skin
low blood sugar level
pleural effusion
pulmonary emboli, or blood clots in the arteries of the lungs
severe ascites
A Mesothelioma does not
usually spread to the bone, brain, or adrenal glands. Pleural tumors
are usually found only on one side of the lungs.
Diagnosing Mesothelioma
is often difficult, because the symptoms are similar to those of a
number of other conditions. Diagnosis begins with a review of the
patient's medical history. A history of exposure to Asbestos may
increase clinical suspicion for mesothelioma. A physical examination
is performed, followed by chest X-ray and often lung function tests.
The X-ray may reveal pleural thickening commonly seen after asbestos
exposure and increases suspicion of Mesothelioma A CT (or CAT)
scan or an MRI is usually performed. If a large amount of fluid is
present, abnormal cells may be detected by cytology if this fluid is
aspirated with a syringe. For pleural fluid this is done by a pleural
tap or chest drain, in ascites with an paracentesis or ascitic drain
and in a pericardial effusion with pericardiocentesis. While absence
of malignant cells on cytology does not completely exclude
mesothelioma, it makes it much more unlikely, especially if an
alternative diagnosis can be made (e.g. tuberculosis, heart failure).
If cytology is positive or a plaque is regarded as suspicious, a
biopsy is needed to confirm a diagnosis of Mesothelioma A doctor
removes a sample of tissue for examination under a microscope by a
pathologist. A biopsy may be done in different ways, depending on
where the abnormal area is located. If the cancer is in the chest, the
doctor may perform a thoracoscopy. In this procedure, the doctor makes
a small cut through the chest wall and puts a thin, lighted tube
called a thoracoscope into the chest between two ribs. Thoracoscopy
allows the doctor to look inside the chest and obtain tissue samples.
If the cancer is in the abdomen, the doctor may perform a laparoscopy.
To obtain tissue for examination, the doctor makes a small incision in
the abdomen and inserts a special instrument into the abdominal
cavity. If these procedures do not yield enough tissue, more extensive
diagnostic surgery may be necessary
The mesothelium consists of a single layer of flattened to cuboidal
cells forming the epithelial lining of the serous cavities of the body
including the peritoneal, pericardial and pleural cavities. Deposition
of asbestos fibres in the parenchyma of the lung may result in the
penetration of the visceral pleura from where the fibre can then be
carried to the pleural surface, thus leading to the development of
malignant mesothelial plaques. The processes leading to the
development of peritoneal Mesothelioma remain
unresolved, although it has been proposed that Asbestos fibres from
the lung are transported to the abdomen and associated organs via the
lymphatic system. Additionally, Asbestos fibres may be
deposited in
the gut after ingestion of sputum contaminated with Asbestos fibres.
Pleural contamination with Asbestos or other mineral
fibres has been
shown to cause cancer. Long thin asbestos fibers (blue Asbestos,
amphibole fibers) are more potent carcinogens than "feathery fibers"
(chrysotile or white asbestos fibers).[6] However, there is now
evidence that smaller particles may be more dangerous than the larger
fibers. They remain suspended in the air where they can be inhaled,
and may penetrate more easily and deeper into the lungs. "We probably
will find out a lot more about the health aspects of Asbestos from
[the World Trade Center attack], unfortunately," said Dr. Alan Fein,
chief of pulmonary and critical-care medicine at North Shore-Long
Island Jewish Health System. Dr. Fein has treated several patients for
"World Trade Center syndrome" or respiratory ailments from brief
exposures of only a day or two near the collapsed buildings.
Mesothelioma development
in rats has been demonstrated following intra-pleural inoculation of
phosphorylated chrysotile fibres. It has been suggested that in
humans, transport of fibres to the pleura is critical to the
pathogenesis of mesothelioma. This is supported by the observed
recruitment of significant numbers of macrophages and other cells of
the immune system to localised lesions of accumulated asbestos fibres
in the pleural and peritoneal cavities of rats. These lesions
continued to attract and accumulate macrophages as the disease
progressed, and cellular changes within the lesion culminated in a
morphologically malignant tumour.
Experimental evidence suggests that asbestos acts as a complete
carcinogen with the development of Mesothelioma occurring in
sequential stages of initiation and promotion. The molecular
mechanisms underlying the malignant transformation of normal
mesothelial cells by Asbestos fibres remain
unclear despite the
demonstration of its oncogenic capabilities. However, complete in
vitro transformation of normal human mesothelial cells to malignant
phenotype following exposure to asbestos fibres has not yet been
achieved. In general, asbestos fibres are thought to act through
direct physical interactions with the cells of the mesothelium in
conjunction with indirect effects following interaction with
inflammatory cells such as macrophages.
Analysis of the interactions between Asbestos fibres and DNA has
shown
that phagocytosed fibres are able to make contact with chromosomes,
often adhering to the chromatin fibres or becoming entangled within
the chromosome. This contact between the Asbestos fibre and the
chromosomes or structural proteins of the spindle apparatus can induce
complex abnormalities. The most common abnormality is monosomy of
chromosome 22. Other frequent abnormalities include structural
rearrangement of 1p, 3p, 9p and 6q chromosome arms.
Asbestos has also been shown to mediate the entry of foreign DNA into
target cells. Incorporation of this foreign DNA may lead to mutations
and oncogenesis by several possible mechanisms:
Inactivation of tumor suppressor genes
Activation of oncogenes
Activation of proto-oncogenes due to incorporation of foreign DNA
containing a promoter region
Activation of DNA repair enzymes, which may be prone to error
Activation of telomerase
Prevention of apoptosis
Asbestos fibers have been shown to alter the function and secretory
properties of macrophages, ultimately creating conditions which favour
the development of mesothelioma. Following asbestos phagocytosis,
macrophages generate increased amounts of hydroxyl radicals, which are
normal by-products of cellular anaerobic metabolism. However, these
free radicals are also known clastogenic and membrane-active agents
thought to promote Asbestos carcinogenicity.
These oxidants can
participate in the oncogenic process by directly and indirectly
interacting with DNA, modifying membrane-associated cellular events,
including oncogene activation and perturbation of cellular antioxidant
defences.
Asbestos also may possess
immunosuppressive properties. For example,
chrysotile fibres have been shown to depress the in vitro
proliferation of phytohemagglutinin-stimulated peripheral blood
lymphocytes, suppress natural killer cell lysis and significantly
reduce lymphokine-activated killer cell viability and recovery.
Furthermore, genetic alterations in asbestos-activated macrophages may
result in the release of potent mesothelial cell mitogens such as
platelet-derived growth factor (PDGF) and transforming growth factor
which in turn, may induce the chronic stimulation and proliferation of
mesothelial cells after injury by Asbestos fibres
Incidence
Although reported incidence rates have increased in the past 20 years,
mesothelioma is still a relatively rare cancer. The incidence rate is
approximately one per 1,000,000. The highest incidence is found in
Britain, Australia and Belgium: 30 per 1,000,000 per year.[7] For
comparison, populations with high levels of smoking can have a lung
cancer incidence of over 1,000 per 1,000,000. Incidence of malignant
Mesothelioma currently
ranges from about 7 to 40 per 1,000,000 in industrialized Western
nations, depending on the amount of asbestos exposure of the
populations during the past several decades.[8] It has been estimated
that incidence may have peaked at 15 per 1,000,000 in the United
States in 2004. Incidence is expected to continue increasing in other
parts of the world. Mesothelioma occurs more
often in men than in women and risk increases with age, but this
disease can appear in either men or women at any age. Approximately
one fifth to one third of all mesotheliomas are peritoneal.
Between 1940 and 1979, approximately 27.5 million people were
occupationally exposed to asbestos in the United States [4]. Between
1973 and 1984, there has been a threefold increase in the diagnosis of
pleural Mesothelioma in
Caucasian males. From 1980 to the late 1990s, the death rate from Mesothelioma in the USA
increased from 2,000 per year to 3,000, with men four times more
likely to acquire it than women. These rates may not be accurate,
since it is possible that many cases of Mesothelioma are
misdiagnosed as adenocarcinoma of the lung, which is difficult to
differentiate from mesothelioma.
Risk factors
Working with Asbestos is
the major risk factor for Mesothelioma A history of
Asbestos exposure exists
in almost all cases. However, Mesothelioma has been
reported in some individuals without any known exposure to asbestos.
In rare cases, Mesothelioma has also been
associated with irradiation, intrapleural thorium dioxide
(Thorotrast), and inhalation of other fibrous silicates, such as
erionite.
Asbestos is the name of a
group of minerals that occur naturally as
masses of strong, flexible fibers that can be separated into thin
threads and woven. Asbestos has been widely
used in many industrial
products, including cement, brake linings, roof shingles, flooring
products, textiles, and insulation. If tiny Asbestos particles float
in the air, especially during the manufacturing process, they may be
inhaled or swallowed, and can cause serious health problems. In
addition to Mesothelioma,
exposure to Asbestos
increases the risk of lung cancer, Asbestos (a
noncancerous, chronic lung ailment), and other cancers, such as those
of the larynx and kidney.
The combination of smoking and Asbestos exposure
significantly
increases a person's risk of developing cancer of the airways (lung
cancer, bronchial carcinoma). The Kent brand of cigarettes used
asbestos in its filters for the first few years of production in the
1950s and some cases of Mesothelioma have resulted.
Smoking modern cigarettes does not appear to increase the risk of
mesothelioma.
Some studies suggest that simian virus 40 (SV40) may act as a cofactor
in the development of Mesothelioma
Exposure
Asbestos was known in
antiquity, but it wasn't mined and widely used
commercially until the late 1800s. Its use greatly increased during
World War II. Since the early 1940s, millions of American workers have
been exposed to Asbestos
dust. Initially, the risks associated with
Asbestos exposure were
not publicly known. However, an increased risk
of developing Mesothelioma was later found
among shipyard workers, people who work in asbestos mines and mills,
producers of Asbestos
products, workers in the heating and
construction industries, and other tradespeople. Today, the U.S.
Occupational Safety and Health Administration (OSHA) sets limits for
acceptable levels of Asbestos exposure in the
workplace, and created
guidelines for engineering controls and respirators, protective
clothing, exposure monitoring, hygiene facilities and practices,
warning signs, labeling, recordkeeping, and medical exams. By
contrast, the British Government's Health and Safety Executive (HSE)
states formally that any threshold for Mesothelioma must be at a
very low level and it is widely agreed that if any such threshold does
exist at all, then it cannot currently be quantified. For practical
purposes, therefore, HSE does not assume that any such threshold
exists. People who work with asbestos wear personal protective
equipment to lower their risk of exposure. Recent findings have shown
that a mineral called erionite has been known to cause genetically
pre-dispositioned individuals to have malignant Mesothelioma rates much
higher than those not pre-dispositioned genetically. A study in
Cappadocia, Turkey has shown that 3 villiages in Turkey have death
rates of 51% attributed to erionite related mesothelioma.
Occupational
Exposure to Asbestos
fibres has been recognised as an occupational
health hazard since the early 1900s. Several epidemiological studies
have associated exposure to Asbestos with the
development of lesions
such as Asbestos bodies
in the sputum, pleural plaques, diffuse
pleural thickening, asbestosis, carcinoma of the lung and larynx,
gastrointestinal tumours, and diffuse Mesothelioma of the pleura
and peritoneum.
The documented presence of Asbestos fibres in water
supplies and food
products has fostered concerns about the possible impact of long-term
and, as yet, unknown exposure of the general population to these
fibres. Although many authorities consider brief or transient exposure
to asbestos fibres as inconsequential and an unlikely risk factor,
some epidemiologists claim that there is no risk threshold. Cases of
Mesothelioma have been
found in people whose only exposure was breathing the air through
ventilation systems. Other cases had very minimal (3 months or less)
direct exposure.
Commercial asbestos mining at Wittenoom, Western Australia, occurred
between 1945 and 1966. A cohort study of miners employed at the mine
reported that while no deaths occurred within the first 10 years after
crocidolite exposure, 85 deaths attributable to Mesothelioma had occurred by
1985. By 1994, 539 reported deaths due to mesothelioma had been
reported in Western Australia.
Paraoccupational secondary exposure
Family members and others living with Asbestos workers have an
increased risk of developing Legalfactz and possibly
other Asbestos related
diseases. This risk may be the result of
exposure to Asbestos dust
brought home on the clothing and hair of
asbestos workers. To reduce the chance of exposing family members to
asbestos fibres, Asbestos
workers are usually required to shower and
change their clothing before leaving the workplace.
Asbestos in buildings
Many building materials used in both public and domestic premises
prior to the banning of Asbestos may contain
asbestos. Those
performing renovation works or DIY activities may expose themselves to
asbestos dust. In the UK use of Chrysotile asbestos was banned at the
end of 1999. Brown and blue Asbestos was banned in the
UK around 1985.
Buildings built or renovated prior to these dates may contain Asbestos
materials.
Environmental exposures
Incidence of mesothelioma had been found to be higher in populations
living near naturally occurring asbestos. For example, in Cappadocia,
Turkey, an unprecedented Mesothelioma epidemic caused
50% of all deaths in three small villages. Initially, this was
attributed to erionite, however, recently, it has been shown that
erionite causes mesothelioma mostly in families with a genetic
predisposition
Treatment of malignant Mesothelioma using
conventional therapies in combination with radiation and or
chemotherapy on stage I or II Mesothelioma have proved on
average 74.6 percent successful in extending the patients life span by
five years or more [commonly known as remission][this percentage may
increases or decrease depending on date of discovery / stage of
malignant development] (Oncology Today, 2009). Treatment course is
primarily determined by the staging or development. This is unlike
traditional treatment such as surgery by itself which has proved only
be 16.3 percent likely to extend a patients life span by five years or
more [commonly known as remission]. Clinical behavior of the
malignancy is affected by several factors including the continuous
mesothelial surface of the pleural cavity which favors local
metastasis via exfoliated cells, invasion to underlying tissue and
other organs within the pleural cavity, and the extremely long latency
period between Asbestos
exposure and development of the disease
Asbestos
Mesothelioma is a form of
cancer that is almost always caused by previous exposure to Asbestos.
In this disease, malignant cells develop in the mesothelium, a
protective lining that covers most of the body's internal organs. Its
most common site is the pleura (outer lining of the lungs and internal
chest wall), but it may also occur in the peritoneum (the lining of
the abdominal cavity), the heart, the pericardium (a sac that
surrounds the heart) or tunica vaginalis.
Most people who develop Mesothelioma have worked on
jobs where they inhaled Asbestos particles, or they
have been exposed
to Asbestos dust and
fiber in other ways. Washing the clothes of a
family member who worked with asbestos can also put a person at risk
for developing mesothelioma. Unlike lung cancer, there is no
association between Mesothelioma and smoking.
Compensation via Asbestos
funds or lawsuits is an important issue in
mesothelioma (see Asbestos and the law).
The symptoms of Mesothelioma include
shortness of breath due to pleural effusion (fluid between the lung
and the chest wall) or chest wall pain, and general symptoms such as
weight loss. The diagnosis may be suspected with chest X-ray and CT
scan, and is confirmed with a biopsy (tissue sample) and microscopic
examination. A thoracoscopy (inserting a tube with a camera into the
chest) can be used to take biopsies. It allows the introduction of
substances such as talc to obliterate the pleural space (called
pleurodesis), which prevents more fluid from accumulating and pressing
on the lung. Despite treatment with chemotherapy, radiation therapy or
sometimes surgery, the disease carries a poor prognosis. Research
about screening tests for the early detection of mesothelioma is
ongoing.
Symptoms of Mesothelioma
may not appear until 20 to 50 years after exposure to Asbestos.
Shortness of breath, cough, and pain in the chest due to an
accumulation of fluid in the pleural space are often symptoms of
pleuralMesothelioma
Symptoms of peritoneal Mesothelioma include weight
loss and cachexia, abdominal swelling and pain due to ascites (a
buildup of fluid in the abdominal cavity). Other symptoms of
peritoneal Mesothelioma
may include bowel obstruction, blood clotting abnormalities, anemia,
and fever. If the cancer has spread beyond the mesothelium to other
parts of the body, symptoms may include pain, trouble swallowing, or
swelling of the neck or face.
These symptoms may be caused by Mesothelioma or by other,
less serious conditions.
Mesothelioma that affects
the pleura can cause these signs and symptoms:
chest wall pain
pleural effusion, or fluid surrounding the lung
shortness of breath
fatigue or anemia
wheezing, hoarseness, or cough
blood in the sputum (fluid) coughed up (hemoptysis)
In severe cases, the person may have many tumor masses. The individual
may develop a pneumothorax, or collapse of the lung. The disease may
metastasize, or spread, to other parts of the body.
Tumors that affect the abdominal cavity often do not cause symptoms
until they are at a late stage. Symptoms include:
abdominal pain
ascites, or an abnormal buildup of fluid in the abdomen
a mass in the abdomen
problems with bowel function
weight loss
In severe cases of the disease, the following signs and symptoms may be present:
blood clots in the veins, which may cause thrombophlebitis
disseminated intravascular coagulation, a disorder causing severe
bleeding in many body organs
jaundice, or yellowing of the eyes and skin
low blood sugar level
pleural effusion
pulmonary emboli, or blood clots in the arteries of the lungs
severe ascites
A Mesothelioma does not
usually spread to the bone, brain, or adrenal glands. Pleural tumors
are usually found only on one side of the lungs.
Diagnosing Mesothelioma
is often difficult, because the symptoms are similar to those of a
number of other conditions. Diagnosis begins with a review of the
patient's medical history. A history of exposure to Asbestos may
increase clinical suspicion for mesothelioma. A physical examination
is performed, followed by chest X-ray and often lung function tests.
The X-ray may reveal pleural thickening commonly seen after asbestos
exposure and increases suspicion of Mesothelioma A CT (or CAT)
scan or an MRI is usually performed. If a large amount of fluid is
present, abnormal cells may be detected by cytology if this fluid is
aspirated with a syringe. For pleural fluid this is done by a pleural
tap or chest drain, in ascites with an paracentesis or ascitic drain
and in a pericardial effusion with pericardiocentesis. While absence
of malignant cells on cytology does not completely exclude
mesothelioma, it makes it much more unlikely, especially if an
alternative diagnosis can be made (e.g. tuberculosis, heart failure).
If cytology is positive or a plaque is regarded as suspicious, a
biopsy is needed to confirm a diagnosis of Mesothelioma A doctor
removes a sample of tissue for examination under a microscope by a
pathologist. A biopsy may be done in different ways, depending on
where the abnormal area is located. If the cancer is in the chest, the
doctor may perform a thoracoscopy. In this procedure, the doctor makes
a small cut through the chest wall and puts a thin, lighted tube
called a thoracoscope into the chest between two ribs. Thoracoscopy
allows the doctor to look inside the chest and obtain tissue samples.
If the cancer is in the abdomen, the doctor may perform a laparoscopy.
To obtain tissue for examination, the doctor makes a small incision in
the abdomen and inserts a special instrument into the abdominal
cavity. If these procedures do not yield enough tissue, more extensive
diagnostic surgery may be necessary
The mesothelium consists of a single layer of flattened to cuboidal
cells forming the epithelial lining of the serous cavities of the body
including the peritoneal, pericardial and pleural cavities. Deposition
of asbestos fibres in the parenchyma of the lung may result in the
penetration of the visceral pleura from where the fibre can then be
carried to the pleural surface, thus leading to the development of
malignant mesothelial plaques. The processes leading to the
development of peritoneal Mesothelioma remain
unresolved, although it has been proposed that Asbestos fibres from
the lung are transported to the abdomen and associated organs via the
lymphatic system. Additionally, Asbestos fibres may be
deposited in
the gut after ingestion of sputum contaminated with Asbestos fibres.
Pleural contamination with Asbestos or other mineral
fibres has been
shown to cause cancer. Long thin asbestos fibers (blue Asbestos,
amphibole fibers) are more potent carcinogens than "feathery fibers"
(chrysotile or white asbestos fibers).[6] However, there is now
evidence that smaller particles may be more dangerous than the larger
fibers. They remain suspended in the air where they can be inhaled,
and may penetrate more easily and deeper into the lungs. "We probably
will find out a lot more about the health aspects of Asbestos from
[the World Trade Center attack], unfortunately," said Dr. Alan Fein,
chief of pulmonary and critical-care medicine at North Shore-Long
Island Jewish Health System. Dr. Fein has treated several patients for
"World Trade Center syndrome" or respiratory ailments from brief
exposures of only a day or two near the collapsed buildings.
Mesothelioma development
in rats has been demonstrated following intra-pleural inoculation of
phosphorylated chrysotile fibres. It has been suggested that in
humans, transport of fibres to the pleura is critical to the
pathogenesis of mesothelioma. This is supported by the observed
recruitment of significant numbers of macrophages and other cells of
the immune system to localised lesions of accumulated asbestos fibres
in the pleural and peritoneal cavities of rats. These lesions
continued to attract and accumulate macrophages as the disease
progressed, and cellular changes within the lesion culminated in a
morphologically malignant tumour.
Experimental evidence suggests that asbestos acts as a complete
carcinogen with the development of Mesothelioma occurring in
sequential stages of initiation and promotion. The molecular
mechanisms underlying the malignant transformation of normal
mesothelial cells by Asbestos fibres remain
unclear despite the
demonstration of its oncogenic capabilities. However, complete in
vitro transformation of normal human mesothelial cells to malignant
phenotype following exposure to asbestos fibres has not yet been
achieved. In general, asbestos fibres are thought to act through
direct physical interactions with the cells of the mesothelium in
conjunction with indirect effects following interaction with
inflammatory cells such as macrophages.
Analysis of the interactions between Asbestos fibres and DNA has
shown
that phagocytosed fibres are able to make contact with chromosomes,
often adhering to the chromatin fibres or becoming entangled within
the chromosome. This contact between the Asbestos fibre and the
chromosomes or structural proteins of the spindle apparatus can induce
complex abnormalities. The most common abnormality is monosomy of
chromosome 22. Other frequent abnormalities include structural
rearrangement of 1p, 3p, 9p and 6q chromosome arms.
Asbestos has also been shown to mediate the entry of foreign DNA into
target cells. Incorporation of this foreign DNA may lead to mutations
and oncogenesis by several possible mechanisms:
Inactivation of tumor suppressor genes
Activation of oncogenes
Activation of proto-oncogenes due to incorporation of foreign DNA
containing a promoter region
Activation of DNA repair enzymes, which may be prone to error
Activation of telomerase
Prevention of apoptosis
Asbestos fibers have been shown to alter the function and secretory
properties of macrophages, ultimately creating conditions which favour
the development of mesothelioma. Following asbestos phagocytosis,
macrophages generate increased amounts of hydroxyl radicals, which are
normal by-products of cellular anaerobic metabolism. However, these
free radicals are also known clastogenic and membrane-active agents
thought to promote Asbestos carcinogenicity.
These oxidants can
participate in the oncogenic process by directly and indirectly
interacting with DNA, modifying membrane-associated cellular events,
including oncogene activation and perturbation of cellular antioxidant
defences.
Asbestos also may possess
immunosuppressive properties. For example,
chrysotile fibres have been shown to depress the in vitro
proliferation of phytohemagglutinin-stimulated peripheral blood
lymphocytes, suppress natural killer cell lysis and significantly
reduce lymphokine-activated killer cell viability and recovery.
Furthermore, genetic alterations in asbestos-activated macrophages may
result in the release of potent mesothelial cell mitogens such as
platelet-derived growth factor (PDGF) and transforming growth factor
which in turn, may induce the chronic stimulation and proliferation of
mesothelial cells after injury by Asbestos fibres
Incidence
Although reported incidence rates have increased in the past 20 years,
mesothelioma is still a relatively rare cancer. The incidence rate is
approximately one per 1,000,000. The highest incidence is found in
Britain, Australia and Belgium: 30 per 1,000,000 per year.[7] For
comparison, populations with high levels of smoking can have a lung
cancer incidence of over 1,000 per 1,000,000. Incidence of malignant
Mesothelioma currently
ranges from about 7 to 40 per 1,000,000 in industrialized Western
nations, depending on the amount of asbestos exposure of the
populations during the past several decades.[8] It has been estimated
that incidence may have peaked at 15 per 1,000,000 in the United
States in 2004. Incidence is expected to continue increasing in other
parts of the world. Mesothelioma occurs more
often in men than in women and risk increases with age, but this
disease can appear in either men or women at any age. Approximately
one fifth to one third of all mesotheliomas are peritoneal.
Between 1940 and 1979, approximately 27.5 million people were
occupationally exposed to asbestos in the United States [4]. Between
1973 and 1984, there has been a threefold increase in the diagnosis of
pleural Mesothelioma in
Caucasian males. From 1980 to the late 1990s, the death rate from Mesothelioma in the USA
increased from 2,000 per year to 3,000, with men four times more
likely to acquire it than women. These rates may not be accurate,
since it is possible that many cases of Mesothelioma are
misdiagnosed as adenocarcinoma of the lung, which is difficult to
differentiate from mesothelioma.
Risk factors
Working with Asbestos is
the major risk factor for Mesothelioma A history of
Asbestos exposure exists
in almost all cases. However, Mesothelioma has been
reported in some individuals without any known exposure to asbestos.
In rare cases, Mesothelioma has also been
associated with irradiation, intrapleural thorium dioxide
(Thorotrast), and inhalation of other fibrous silicates, such as
erionite.
Asbestos is the name of a
group of minerals that occur naturally as
masses of strong, flexible fibers that can be separated into thin
threads and woven. Asbestos has been widely
used in many industrial
products, including cement, brake linings, roof shingles, flooring
products, textiles, and insulation. If tiny Asbestos particles float
in the air, especially during the manufacturing process, they may be
inhaled or swallowed, and can cause serious health problems. In
addition to Mesothelioma,
exposure to Asbestos
increases the risk of lung cancer, Asbestos (a
noncancerous, chronic lung ailment), and other cancers, such as those
of the larynx and kidney.
The combination of smoking and Asbestos exposure
significantly
increases a person's risk of developing cancer of the airways (lung
cancer, bronchial carcinoma). The Kent brand of cigarettes used
asbestos in its filters for the first few years of production in the
1950s and some cases of Mesothelioma have resulted.
Smoking modern cigarettes does not appear to increase the risk of
mesothelioma.
Some studies suggest that simian virus 40 (SV40) may act as a cofactor
in the development of Mesothelioma
Exposure
Asbestos was known in
antiquity, but it wasn't mined and widely used
commercially until the late 1800s. Its use greatly increased during
World War II. Since the early 1940s, millions of American workers have
been exposed to Asbestos
dust. Initially, the risks associated with
Asbestos exposure were
not publicly known. However, an increased risk
of developing Mesothelioma was later found
among shipyard workers, people who work in asbestos mines and mills,
producers of Asbestos
products, workers in the heating and
construction industries, and other tradespeople. Today, the U.S.
Occupational Safety and Health Administration (OSHA) sets limits for
acceptable levels of Asbestos exposure in the
workplace, and created
guidelines for engineering controls and respirators, protective
clothing, exposure monitoring, hygiene facilities and practices,
warning signs, labeling, recordkeeping, and medical exams. By
contrast, the British Government's Health and Safety Executive (HSE)
states formally that any threshold for Mesothelioma must be at a
very low level and it is widely agreed that if any such threshold does
exist at all, then it cannot currently be quantified. For practical
purposes, therefore, HSE does not assume that any such threshold
exists. People who work with asbestos wear personal protective
equipment to lower their risk of exposure. Recent findings have shown
that a mineral called erionite has been known to cause genetically
pre-dispositioned individuals to have malignant Mesothelioma rates much
higher than those not pre-dispositioned genetically. A study in
Cappadocia, Turkey has shown that 3 villiages in Turkey have death
rates of 51% attributed to erionite related mesothelioma.
Occupational
Exposure to Asbestos
fibres has been recognised as an occupational
health hazard since the early 1900s. Several epidemiological studies
have associated exposure to Asbestos with the
development of lesions
such as Asbestos bodies
in the sputum, pleural plaques, diffuse
pleural thickening, asbestosis, carcinoma of the lung and larynx,
gastrointestinal tumours, and diffuse Mesothelioma of the pleura
and peritoneum.
The documented presence of Asbestos fibres in water
supplies and food
products has fostered concerns about the possible impact of long-term
and, as yet, unknown exposure of the general population to these
fibres. Although many authorities consider brief or transient exposure
to asbestos fibres as inconsequential and an unlikely risk factor,
some epidemiologists claim that there is no risk threshold. Cases of
Mesothelioma have been
found in people whose only exposure was breathing the air through
ventilation systems. Other cases had very minimal (3 months or less)
direct exposure.
Commercial asbestos mining at Wittenoom, Western Australia, occurred
between 1945 and 1966. A cohort study of miners employed at the mine
reported that while no deaths occurred within the first 10 years after
crocidolite exposure, 85 deaths attributable to Mesothelioma had occurred by
1985. By 1994, 539 reported deaths due to mesothelioma had been
reported in Western Australia.
Paraoccupational secondary exposure
Family members and others living with Asbestos workers have an
increased risk of developing Legalfactz and possibly
other Asbestos related
diseases. This risk may be the result of
exposure to Asbestos dust
brought home on the clothing and hair of
asbestos workers. To reduce the chance of exposing family members to
asbestos fibres, Asbestos
workers are usually required to shower and
change their clothing before leaving the workplace.
Asbestos in buildings
Many building materials used in both public and domestic premises
prior to the banning of Asbestos may contain
asbestos. Those
performing renovation works or DIY activities may expose themselves to
asbestos dust. In the UK use of Chrysotile asbestos was banned at the
end of 1999. Brown and blue Asbestos was banned in the
UK around 1985.
Buildings built or renovated prior to these dates may contain Asbestos
materials.
Environmental exposures
Incidence of mesothelioma had been found to be higher in populations
living near naturally occurring asbestos. For example, in Cappadocia,
Turkey, an unprecedented Mesothelioma epidemic caused
50% of all deaths in three small villages. Initially, this was
attributed to erionite, however, recently, it has been shown that
erionite causes mesothelioma mostly in families with a genetic
predisposition
Treatment of malignant Mesothelioma using
conventional therapies in combination with radiation and or
chemotherapy on stage I or II Mesothelioma have proved on
average 74.6 percent successful in extending the patients life span by
five years or more [commonly known as remission][this percentage may
increases or decrease depending on date of discovery / stage of
malignant development] (Oncology Today, 2009). Treatment course is
primarily determined by the staging or development. This is unlike
traditional treatment such as surgery by itself which has proved only
be 16.3 percent likely to extend a patients life span by five years or
more [commonly known as remission]. Clinical behavior of the
malignancy is affected by several factors including the continuous
mesothelial surface of the pleural cavity which favors local
metastasis via exfoliated cells, invasion to underlying tissue and
other organs within the pleural cavity, and the extremely long latency
period between Asbestos
exposure and development of the disease
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