Diseases

CANCER

The first cancer experiments took place in 1910

Peyton Rous took chicken tumor cells and was able to “infect” healthy chicken cells

Scientists couldn’t explain the reasoning for this because so many different things seemed to be associated with cancer

In 1700, an Italian physician wrote about the high rate of breast cancer among nuns and speculated that it was related to their celibacy and childlessness

This was the first indication that how one lived might affect the development of cancer

In 1775, a London physician, suggest that the very high rate of scrotal and nasal cancers among chimney sweeps was a result of their exposure to soot

This was the first indication that exposure to certain chemicals could lead to cancer

In 1886, a professor at the Medical School in Rio de Janeiro, reported the case of a family with an increased susceptibility to retinoblastoma, a form of cancer that normally occurs in only one out of about 20,000 children

This was the first indication that cancers have a hereditary basis

The discovery of x-rays in 1895 led to its association with the skin cancer on the hand of a lab technician by 1902. Within a decade, many more physicians and scientists, unaware of the dangers of radiation, developed a variety of cancers

In 1907, an epidemiological study found that the meat-eating Germans, Irish, and Scandinavians living in Chicago had higher rates of cancer than did Italians and Chinese who ate considerably less meat

First indication that your home environment can cause cancer

“Tumors destroy man in a unique and appalling way, as flesh of his own flesh which has somehow been rendered proliferative, rampant, predatory, and ungovernable…Yet, despite more than 70 years of experimental study, they remain the least understood…What can be the why for these happenings?”

Peyton Rous, in Nobel Prize Acceptance Speech 1966

Much research has been done to answer Peyton Rous’ question of why cancer happens

Cancer develops when mutations occur in genes that normally operate to control cell division

Mutations can be caused by a wide variety of environmental agents, viruses, and inheritance

What is cancer?

Cancer is a group of more than 100 diseases that develop across time and involve the uncontrolled division of the body’s cells

Cancer can develop in any of the body’s tissues and each type of cancer is unique but the basic processes that produce cancer are similar in all forms of the disease

Cancer begins when a cell breaks free from the normal restraints on cell division and begins to follow its own agenda for proliferating

All of the cells produced from the first mutated cell also divide inappropriately creating a tumor

A tumor, or mass of cells, formed of these abnormal cells may remain within the tissue in which it originated or it may invade nearby tissues

An invasive tumor (cells that invade nearby tissues) is said to be malignant

Cells of malignant tumors can create tumors in other parts of the body by traveling through the blood

Body's Defenses

In order to prevent cancer, your body has three lines of defense

1. DNA repair mechanisms – when DNA is replicated it is checked to make sure it was copied correctly. If not then the cell does not move on in the cell cycle until the correction is fixed

2. Apoptosis – ‘cell suicide’ if something is wrong in the cell, the cell will ‘kill itself’

3. Cells have a fixed number of divisions – this assures cells cannot reproduce endlessly

Let’s review the cell cycle so we can see where the body’s defenses come into play

Interphase consists of 3 stages:

G1 – Growth 1

S – Synethesis (DNA replication)

G2 – Growth 2

Mitosis consists of 4 Stages:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

The first defense acts directly on the DNA

As DNA replicates, it is being checked for mutations

Apoptosis is regulated cell death

If a major component of the cell is damaged or if the control system is deregulated, the cell will ‘kill itself’

It sends signals out to surrounding phagocytes that will digest the cell and get rid of it

Apoptosis can also occur during the cell cycle if the damage is extreme

The cell cycle has 3 checkpoints:

Mitosis

Finally, cells have a fixed number of divisions

As they divide, the telomeres shorten, when they shorten enough the cell can no longer replicate

Early observations suggested that certain life styles were responsible for cancer because life styles exposed people to certain chemicals

But then there was also the fact that cancer can be hereditary

These facts confused scientists because so many chemicals could eventually cause cancer

The variety of observations also allowed scientists to figure out how cancer comes to be

For example, when Rous transferred tumor chicken cells into healthy chicken cells, displayed to scientists that cancer can be traced simply and definitely back to a single cause

Rous’ work forced scientists to research cancer at the cellular level (DNA and cell cycle)

Cell biologists studied cells by observing them in the lab and creating inferences from their appearance in the whole organism

This approach allowed doctors to realize that tumors arise from one’s own tissues, not from cells introduced into the body by infection

Cell biology has also discovered that tumors are monoclonal, meaning that tumors arise from one type of normal cells

There are two scenarios that describe this.

The first scenario:

Many individual cells become cancerous and the tumor is a result of these original cells

The second scenario:

One cell becomes abnormal and the tumor is a result of the decedents of that one cell

Again, cancer is a disease which a single normal body cell undergoes a genetic transformation into a cancer cell

This cell proliferates causing a tumor

It is still difficult to find the exact origin of a tumor because once a tumor forms, the cells display different characteristics

Tumor cells are constantly changing depending on the environment

A second trend found by cell biologists is that cancer cells are very different from normal cells

Cancer cells are unstable and are prone to rearrangements, duplications, and deletions of their chromosomes

Because of these characteristics, all cancer cells display unusual and different traits

The nucleus of normal cells is 1/5 the size of the cell, the nucleus in cancer cells occupies most of cell’s volume

Because of the mutations, tumor cells have different traits from their original cell

For example: Normal secretory cells produce and release mucus. Cancer cells may no longer do this

The key difference between cancer and normal cells is that cancer cells have lost restraints on growth that characterize normal cells

A large number of tumor cells are engaged in mitosis while normal cells rarely go through mitosis

Through all this research, scientists were able to create a unified view of cancer in the 1970s

Cancer begins because carcinogens (cancer causing agents) induce mutations in critical genes and these mutations direct the cell and its offspring to grow abnormally

The result of this abnormal growth appears years later as a tumor

We now know the body’s defenses against cancer

Because of these defenses, cancer does not develop at once from a mutation of one or two genes

Instead it develops step-by-step, across time, as an accumulation of many molecular changes

Tumors generally consist of 10 billion to 100 billion cells

It can take years before this happens and then spreads to other parts of the body

Understanding cancer as a multistep process explains many observations

This explains why cancer occurs more often in older people

Older people have experienced a complex and extended succession of events,

Cancer as a multistep event also explains why people who are exposed to carcinogens more often develop cancer

It also explains inheriting a cancer-susceptibility mutation. Instead of the mutation being a rare event, it has already occurred

Finally, it also explains the lag time between the exposure to a cancer-causing agent and the development of cancer

For example, it explains the 20-25 year lag between the onset of lung cancer of women who smoked during World War II

Now we have a basic understanding of what cancer is and how it is caused, let’s look at who is effected by it the most

More than 8 million Americans have a history of cancer

Cancer is the second leading cause of death in the United States, exceeded only by heart disease

Cancer among children is relatively rare

Cancer is the second leading cause of child death

Leukemias and cancer of the brain and other nervous system organs account for more than one-half of the cancer among children

The overall survival rate for all cancer sites combined is increasing

From 1974-1976 there was a 49.3% chance of survival

From 1983-1990 it increased to 53.9%

This increase can be credited to science research and the improvement in detecting cancer

There have been improvements in detecting and diagnosing cancer early

Americans are more aware of symptoms and are cautious

Surgery, radiation, and chemotherapy are being used more specifically based on the type of cancer

There is also ongoing drug research to restore a cancer cell to normalcy

We have been discussing the history of cancer and how scientists discovered it

Now we will discuss society’s role in fighting cancer

The cost of cancer is large

The National Cancer Institute estimates annual costs of cancer at about $107 billion

This includes:

$37 billion for direct medical costs

$11 billion for morbidity costs (morbidity – probability of getting sick)

$59 billion for mortality (death)

The treatment for breast, lung, and prostate cancers account for more than ½ of the direct medical costs

One way to decrease the costs of cancer is to prevent it

Although citizens know the harmful effects of certain lifestyles, people are still not convinced about prevention

This could be because cancer is random and scientists can not pinpoint who will get cancer and who will not

Unhealthful habits also may persist because of the long time that elapses between exposure and actual development of cancer

Because of the lag time scientists have developed four levels on which to prevent cancer

First level of prevention: Individual

Individuals need to take responsibility and live healthier lives

Second level of prevention: Health care Providers

They provide counseling and screening to individuals

Third level of prevention: National

Government impose regulations that help minimize the public’s exposure to carcinogens

Forth level of prevention: International

Actions of individual countries can help prevent world-wide spread

Is it okay for the government to make these decisions for us?

Ethics is the study of good and bad, right and wrong

For our purposes, something that is “right” or“good” fosters the interests of individuals

Something that is “wrong” or “bad” impairs the interests of individuals

Although certain ideas and actions may be ethical in America, they may not be ethical in other countries

For example, developing countries who do not have the resources America does, take different approaches to cancer and different standards for marketing tobacco and other carcinogens

That brings us to the question: is it ethical for the Unites States to prevent the widespread use of tobacco in other countries since tobacco contributes to lung cancer?

Is there any legal and/or ethical way to govern other choices of individuals that contribute to cancer? (Such as poor diet and lack of exercise?)