Heredity and Environment in Relationship to Cancer Clusters

Heredity and environment are the main contributing factors to the development of cancer. Epidemiologists focus on these two areas when studying cancer clusters. Behavior and lifestyle also contribute to cancer risks so they are also included when studying environment.

To establish a connection between an environmental risk factor and a genetic predisposition is difficult. Scientists must study large groups of people over the course of a long period of time to understand the process of carcinogenesis (the process of normal cells becoming cancer cells). This makes establishing the existence of cancer clusters a lengthy process.

The exposure to certain carcinogenics may also not affect health for many years. In the case of asbestos exposure, it often takes decades for mesothelioma to develop after exposure to the substance. Therefore, the cancer cluster was not identified until many years after the initial exposure began.


Researchers have made some discoveries in regards to heredity and cancer. They have determined that all cancers are caused by some form of gene mutation, which causes the gene to perform abnormally.

Some of these abnormalities are present in an individual at birth. These types of gene mutations are passed down from parent to child. Although this is an uncommon source of cancer it does create “inherited susceptibility” or a predisposition to cancer. Inherited susceptibility does not mean cancer will definitely occur in an individual, however it does indicate a condition where, if other exposures and factors exist, cancer may occur.

Cancer clusters can often be suspected within families due to a higher than expected rate of disease within the family. These cases can sometimes be attributed solely to coincidence. Other times these “familial clusters” can be due to inherited susceptibility coupled with environmental factors.

Somatic alterations are changes that occur to genes throughout an individuals lifetime. These alterations are more likely than inherited susceptibility to be the cause of cancer.


Environmental exposures have often been suspected by individuals to be the cause of cancer clusters. The environmental factors that are considered by epidemiologists include the air, water and earth surrounding an individual or group. Other environmental factors that influence cancer clusters are home and workplace conditions, tobacco use, drugs and alcohol, chemical exposures, and exposure to radiation or even sunlight.

Due to varying susceptibility in individuals and the vast array of chemical and other substances in our world identifying specific causes of cancer is extremely difficult.

Workplace discoveries in regards to chemical exposures have provided positive results in the study of dangerous exposures to certain substances. Certain occupational studies have proved the toxicity of chemical carcinogens and led researchers to develop ways of reducing exposure.

Causes of Cancer Clusters

There are many risk factors for cancer in the world today. Smoking, poor diet, lack of exercise and inactivity are some of the preventable cancer risks. Carcinogens in the environment can also cause cancer. Cancer clusters, once identified as such, often may not have an underlying cause.

There are often several explanations when considering cancer clusters including coincidence, external behaviors (smoking) and miscalculation of historic incidences. When these factors do not explain the cancer cluster, a deeper, more thorough study can be conducted. These often take many years and do not always provide a clear and definitive answer.

Epidemiology and Cancer Clusters

Epidemiology is the study of the factors that cause illnesses and disease with in a population. This field of study is critical in the prevention and spread of communicable and non-communicable disease. Epidemiology is used to identify disease from the outbreak through diagnosis and treatment.

Epidemiolgists, those scientists who study the causes of disease, utilize knowledge in biology, sociology and philosophy in an effort to understand and communicate risk factors for disease.

Carcinogenesis, or the process by which normal cells become cancer cells, is studied by epidemiologists to determine the existence of cancer clusters.

Cancer clusters are rare and epidemiologists determine, through specific criteria if and when a cancer cluster exists. Many individuals will report a cancer cluster but it is the job of an epidemiologist to determine if there is an environmental cause for the incidence of cancer or if the high rate of cancer is merely coincidence.

An epidemiologist will utilize several specific criteria to decide if further investigation is necessary in regards to a cancer cluster. When one type of cancer is found in a population in large numbers this may be a warning sign of a cancer cluster. There are over 100 varieties of the disease so it is rare for one, specific type to be found in large numbers in a population.

There are rare forms of cancer and there are more common forms of the disease. If a rare form of cancer is found in high numbers within a community or group this may also signify a cancer cluster.

A third warning sign to the existence of a possible cancer cluster is when a specific age group in an area suffers from a form of cancer that does not usually affect that age group.

In the beginning stages of determining the existence of a cancer cluster, epidemiologists must first assess the health of the individuals affected. If the cancer is a result of an underlying infection or due to the spread of cancer from another area of the body, this individual is not part of a cancer cluster. The primary cancer is the only cancer considered in the study of a cancer cluster.

Epidemiologists will use biological knowledge to study the significance and causes of the particular type of cancer. The scientist will use knowledge of biological causes of disease to determine if exposure to environmental factors has the ability to cause the specific type of cancer.

In the process of deciding whether or not a cancer cluster truly exists it is important for the epidemiologist to define the borders of the geographical area. Often there are cases in outlying areas causing additional individuals to become involved in the study. These situations may create false cancer clusters.

It is very difficult to determine with absolute certainty if the number of cancer cases is higher that what would be normally expected. The use of statistical factors such as age, gender and race are utilized but lifestyle factors may cause the numbers to be different than what would normally be expected.

It is not possible in all cases to make a determination that a cancer cluster does exist. In some situations the cases of cancer are higher than what would normally be expected within the geographical area in the specified time period, however the epidemiologists cannot find an underlying cause for the disease.

In some situations the study of a cancer cluster cannot be completed due to the small amount of subject cases. The epidemiologist must have enough cases of the disease to provide accurate conclusions.

Even in situations when there are many cases, the history of the individuals involved may make specific determinations regarding exposure impossible. For example, an individual may have lived in many areas over the course of a lifetime and determining when and where exposure occurred would then be impossible.

Factors Affecting Cancer Rates

The age of a group of individuals will affect the rate of cancer development. Individuals over the age of 45 have a much greater risk of developing cancer than people younger than 45 years of age. Men and women over the age of 60 have an even greater risk of developing some form of cancer. It would stand to reason that these age groups would have more cases of cancer than other groups in younger age brackets.

Other factors that may affect the rates of cancer development in a particular group are lifestyle behaviors. Individuals with a poor diet may experience a higher cancer rate than those who eat healthfully. A diet rich in vegetables, fruit, lean meats and fish and healthy fats can help prevent cancer in some individuals.

Exercise is also an important part of keeping cancer at bay. Individuals who do not participate in any regular form of exercise are at a greater risk for developing cancer. According to the American Cancer Society one third of all cancer deaths are in some way related to nutrition, obesity, and/or physical inactivity, and could possibly be prevented.

In one study conducted by Dr. Christine Friedenreich, of Alberta Health Services-Alberta Cancer Board in Calgary, Canada, it was discovered that women with breast cancer who had exercised more than four hours per week over their lifetime had a 44 percent lower risk of dying from the disease. Other studies have found similar results with other forms of the disease.

“Greater participation in physical activity has consistently been associated with reduced risk of cancer incidence at several sites, including breast and colon cancers,” said James McClain, Ph.D., cancer prevention fellow at the National Cancer Institute.

Another enormously risky lifestyle behavior is tobacco usage. It is estimated that discontinuing the use of tobacco could prevent one third of all cancers.

These lifestyle factors may cause the incidence of cancer to increase in certain groups such as families or employees that participate in these high-risk behaviors. Cancer clusters may seem to exist however it is lifestyle behaviors, not external environmental carcinogens that cause the unusually high incidence of cancer in these groups.

Cancer Cluster Description and Factors

The term “cancer cluster” describes the condition when the incidence of cancer occurs in higher numbers than expected in a specific geographic area within a particular time frame. These clusters may also be particular to a workplace or a group of people, such as a family.

Families or members of a community often report cancer clusters when cancer is diagnosed in more than one individual in the group. The individuals often feel the need to explain the reason behind the cancer diagnosis and sometimes look at chemicals in the environment to explain the cause of the cancer diagnosis.

It is rare for these cases to be an actual cancer cluster and more often the situation is just coincidental. The forms of cancer are often not even related.

The high incidence of cancer in the United States and worldwide makes it common for individuals in a specific geographic area or even in a shared workplace to get cancer. If the cancer rate continues as it is today at least one in every 10 children born will acquire cancer within their lifetime. This fact could explain the phenomenon of cancer occurring repeatedly in geographic areas or within certain groups of people.

There are over 100  types of cancer. Each form of the disease may have a different cause as well as different rates of occurrence and survival. Some forms of cancer are caused by environmental factors but many others may be caused by genetics and some cases are caused by a combination of both factors. Each type of cancer occurs and reacts in very different ways therefore it is not reasonable to believe a common cause is to blame for every occurrence in a particular group.

Sarcomatoid Mesothelioma Treatment

Sarcomatoid mesothelioma is the least common histological type of mesothelioma, but it is the most aggressive.

Even more than epithelial mesothelioma, the sarcomatoid form is difficult to diagnose and to distinguish from other diseases. Just looking at the cells under a microscope is not enough, and doctors employ immunohistological tests to distinguish Sarcomatoid mesothelioma from true sarcoma and pulmonary sarcomatoid carcinoma.

The general treatment plan for sarcomatoid mesothelioma focuses on:

  • Managing pleural effusions
  • Administering radiotherapy to intervention sites
  • Evaluating suitability for radical surgery
  • Evaluating suitability for chemotherapy and clinical trial entry

Epithelial Mesothelioma – Clinical Presentation and Diagnosis

Epithelial (or epithelioid) mesothelioma is the most common histological type of mesothelioma.  Epithelial mesothelioma is a subtype – both pleural and peritoneal mesothelioma may be epithelial or sarcamatoid or biphasic (including both cell types.)

Epithelial mesothelioma has a better prognosis than other subtypes.  Average life expectancy after diagnosis is longer.

As with all types of mesothelioma, asbestos is the cause.  Most people who get it are men past age 50, although it does occur in younger people and in women.  This is largely because the illness typically does not manifest until decades after initial asbestos exposure.  A significant percentage of patients diagnosed at relatively younger age have experienced asbestos exposure during their childhood.  Approximately 70 to 80 percent of mesothelioma cases involve a male patient. This is due to the fact that men are more likely to be employed at jobs that have a heightened risk for asbestos exposure. Common industries linked to asbestos inhalation include construction, auto repair, shipbuilding and naval employment.


Physical Carcinogenesis

Carcinogenesis is defined as the process of cancer growth. Specifically, the term refers to the process by which normal cells in the body mutate into cancer cells. In order for carcinogenesis to occur, damages in healthy cell DNA must occur. For this reason, carcinogenesis is often tied to genetics. However, exposure to certain chemicals and other hazardous materials can also cause cell damage that can lead to cancer.

Factors That Contribute to Carcinogenesis

While the factors that contribute to cancer growth are complex and still being studied by the research community, a number of contributing factors have been identified that increase a cell’s risk for carcinogenesis. These factors include genetics, environmental exposure and age. Regardless of the instigating cause of cancer growth, proliferation is dependent on the ability of the cancer cells to:

  • Grow quickly and inappropriately
  • Avoid cell death via the body’s defense systems
  • Stimulate their microenvironment
  • Spread to new areas of the body

Based on research, the biological contributing factors that foster carcinogenesis include:

  • Errors in gene expression due to faulty chromatin structure
  • Improper signal transduction between cells
  • Unhealthy hormone exposure
  • Improper metabolism of fatty acid
  • Damaged DNA or repair responses

The Importance of Proto-Oncogenes

Proto-oncogenes are a specific subcategory of genes that are responsible for inducing cell growth. A series of mutations in this key gene category is typically where carcinogenesis begins. Due to one or several of the contributing factors listed above, these proto-oncogenes become damaged in a way that accelerates cell growth. This, in turn, provides the rapid growth necessary for cancer cells to flourish, grow and spread throughout the body at such a rate that the natural immune system cannot adequately defend itself.

Damage to tumor suppressor genes often works in tandem with damaged proto-oncogenes to create cancer. Tumor suppressor genes are designed to clean up any DNA damage that may occur during cell replication. When damage to these tumor suppressors occurs, DNA damage proliferates, which can lead to mutations that ultimately give rise to cancer cells.

Other Instigators of Cancer

Mutation of proto-oncogenes and tumor suppressor genes are thought to be the most common cause of carcinogenesis. However, there are other non-mutagenic effects that also are believed to cause cancer. For example, an increase in estrogen in the body is thought to increase the rate of cell mitosis without causing gene mutation. This increase in mitosis proliferates cell growth much in the same way as damaged proto-oncogenes. Excessive consumption of alcohol can also stimulate mitosis.

To a lesser degree, bacteria and viruses have also been known to spur carcinogenesis. For example, HPV, Hepatitis B and EBV are all known illnesses that can directly cause cancer. It is believed that the reason for this is the virus’ ability to promote cell proliferation by inserting a portion of its own DNA into healthy human cells.

Difference Between Benign and Malignant Tumors

There are three stages of carcinogenesis – initiation, promotion and progression. Initiation results when a cell experiences damaged DNA. Promotion exacerbates cell damage and growth by altering gene expression, suppressing an immune response and enhancing cell division. While in the promotion stage, tumor cells are said to be benign. This means that they are non-cancerous, yet still unhealthy and growing at an abnormal rate.

Once the damaged cells begin to exchange DNA between chromosomes, express oncogenes and exhibit additional mutations, the progression stage of carcinogenesis is achieved. It is in this third stage that malignant tumors begin to grow.


Diagnosing Epithelial Mesothelioma

Performing a concurrent bronchoscopy may be vital for making a differentiation between mesothelioma and metastatic adenocarcinoma of the lung, since endobronchial lesions are seldom seen in mesothelioma.

A new approach to differentiate between mesothelioma and adenocarcinoma of the lung is currently under development. This new approach relies on gene expression profiling, by identifying specific genes that are expressed in malignant mesothelioma but not in case of adenocarcinoma or normal lung tissue.

Particulate Air Pollution

Example: the smokestack of a coal plant ejects coal smoke into the air. Water vapor droplets in the clouds can pick up these smoke particles and drop them later in the form of acid rain.

How is particulate air pollution measured?
Due to the different sizes, shapes and chemical compositions of these microscopic particulate air pollution agents, the task of measuring the potential damage that they can do is often an arduous undertaking. Most agencies involved in pollution research and prevention classify these particles by size: fine particles are less than 2.5 microns (10^-6 m) across and inhalable coarse particles are between 2.5 and 10 microns across. To put these measurements into perspective, a human hair is usually between 70 and 100 microns thick; a red blood cell is about 7 microns across.

What are some other sources of particulate air pollution?

According to a study carried out by the US Environmental Protection Agency (EPA), one of the leading sources of fine particulate air pollution is also the oldest: fires. During 2002, EPA estimates put the quantity of fine particulate air pollution originating from fires at well over one million tons. Since man first learned to create a spark and build fires for light, warmth, and comfort, he has also sent untold tons of untreated, unfiltered smoke into the air. While the concern over particulate air pollution may be a recent occurrence, the sources and the issue itself are both as old as civilization, whether the source is a small campfire or a raging forest blaze.

According to the same study, road dust generated over eight hundred thousand tons of fine particulate air pollution, followed by electricity generation at five hundred thousand. Surprisingly, fossil fuel use (coal, oil, kerosene, gasoline) and automobile usage combined for less than four hundred thousand tons, less than a third of the total for fires.

Of course, air pollution is not limited to outdoor sources. Indoor air pollution can also be a major source of particulate air pollution. Dust, sheet rock particles, cigarette smoke and dirty ventilation systems can create fine particles that can contribute to an increase in indoor particulate air pollution.

Pain Control for Cancer Patients

Defined by pain expert Margo McCaffrey, MSN, RN, FAAN, pain is, “whatever the experiencing person says it is, and exists whenever he says it does.” This certainly holds true in the treatment of pain associated with cancer. Approximately 30% to 50% of all people with cancer will experience pain while undergoing treatment and 70% to 90% of individuals with advanced cancer will have pain associated with the disease.

The good news is that cancer pain is completely manageable with a host of treatments that are readily available. The bad news is that many cancer patients are often under treated for pain due to a variety of common reasons.

Physicians treating cancer patients may focus solely on controlling or treating the disease and the accompanying pain is left untreated. Patients may minimize their pain symptoms or may think the pain is “normal” and neglect to inform the physician of this symptom. In other circumstances patients may fear becoming addicted to pain medications and therefore refuse to take them. These reasons, while understandable, are invalid and the current treatments available can help patients manage their pain.

Each cancer patient will experience different levels and areas of pain. There are three common types of pain associated with cancer. Acute pain usually sets in quickly and lasts only brief amounts of time. Chronic pain is consistent pain that sometimes worsens and lasts for long periods of time. Breakthrough pain occurs in chronic pain sufferers whose pain is normally controlled by medication. The plan for managing this pain is different for each individual. The goal is to provide the best pain relief while avoiding as many side effects as possible.

First-line pain medications are those medicines that are readily available over the counter or by a doctor’s prescription. First-line pain medications are used to treat mild forms of pain associated with cancer and include ibuprofen, aspirin and acetaminophen. These over the counter medications are not usually habit forming and can reduce inflammation in diseased tissue.