Cancer Cell: See What Causes a Cell to Become Cancerous, and Prevention




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WHAT CAUSES A CELL TO BECOME CANCEROUS?

This is a question asked by many people especially students. A cell becomes cancerous majorly due to mutations of some genes known as PROTO-ONCOGENE.
Read on to understand the concept in cell formation as it is much more complex than what is given below.

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INTRODUCTION TO CANCER CELLS

The importance of genetics to life cannot be over-emphasized. Genetics has played a great role in improving the standard of living of humans.


The discovery of genetics has led to the development of a nation’s economy and has challenged nature by reducing the mortality rate and simultaneously increasing the Natality rate.
In the study of genetics, scientists have discovered that there are various genetic diseases majorly caused by MUTATION of a gene called a mutant gene or an oncogene.


Among all the genetic diseases, Cancer is one of the most dangerous. Cancer which is a genetic disease is the second leading cause of death in western countries, surpassed only by heart disease. It strikes people of all ages, and one out of three people has the tendency to experience a cancer diagnosis in his or her lifetime.

Clinically, Cancer is a disease characterized by uncontrolled cell division. It is a genetic disease at the cellular level. More than 100 kinds of human cancer have been identified, and they are classified according to the types of cell that has become cancerous.


Although cancer is a diverse collection of many diseases, some characteristics are common to all cancers. Which are:


1. Most cancers originate in a single cell. This single cell, and its line of daughter cells, undergoes a series of genetic changes that accumulate during cell division. In this regard, a cancerous growth can be considered to be clonal in organ. A hall mark of a cancer cell is that it divides to produce two daughter cancer cells.

2. At the cellular and genetic level, cancer usually is a multistep process that begins with a precancerous genetic change – a benign growth and is followed by additional genetic changes that lead to cancerous cell growth.


3. When cells become cancerous, their growth is described as malignant. Cancer cells are invasive – they can invade healthy tissues – and metastatic – they can migrate to other parts of the body and cause secondary tumors.


Cell biologists now believe that most cancers results from the accumulation of many mutations during the proliferation of somatic cells. When enough mutations accumulate in genes controlling proliferation and other process within a single clone of cells, that clone over grows the normal cells that surrounds it, disseminate through the bloodstream to other parts of the body, and forms a life-threatening tumor or cancer. The large number of phenotypic changes seen in tumor cells suggests that many mutations occurring over time in a single cell then produces a clone of malignant cells. Environmental mutagens are responsible for most cancers; inheritance of certain mutations predisposes some families to development of specific cancers.

CATEGORIES OF CANCER-CAUSING GENES



1. ONCOGENE


This is an abnormally active gene that promotes cancerous growth. A normal, non-mutated gene that has the potential to become an oncogene is called a PROTO-ONCOGENE. To become an oncogene, a proto-oncogene must incur a mutation that causes its expression to be abnormally active. Specific genetic alterations convert proto-oncogenes into oncogenes by isolating and studying oncogenes at the molecular level. These changes can be categorised as follows:


i. Missense mutation: A change in the amino acid sequence of a proto oncogene protein may cause it to function in an abnormal way. Missense mutations can convert ras gene into oncogene.


ii. Gene amplification- The copy number of a proto oncogene may be increased by gene duplication. Myc genes have been amplified in human Leukemias, stomach, lung and colon carcinomas and neuroblastomas and glioblastomas.


iii. Chromosomal translocation: A piece of chromosome may be translocated to another chromosome and affect the expression of genes at the breakpoint site. In Burkitt lymphoma, a region of chromosomes 8 is trans-located to either chromosome 2, 14, or 22. The breakpoint in chromosome 8 causes the over expression of the c myc.

iv. Viral Integration: When a virus integrates into a chromosome, it may enhance the expression of nearby proto oncogenes. In avian lymphomas, the integration of the avian leucosis virus can enhance the transcription of the c-myc gene.


Tumor Suppresor Genes

As the name suggests, the role of d tumor-suppressor gene is to prevent cancerous growth. Therefore, when a tumor suppressor gene becomes inactivated by mutation, it becomes more likely that cancer will occur. It is a loss-of-function in a tumor suppressor gene that promotes cancer.

The first identification of a human tumor suppressor gene was through the studies of Retinoblastosoma, a tumor that occurs in the Retina of the eye.


TYPES OF CANCER CELL


There are various types of cancer which is more than hundred. We cannot exhaust the list of the types of cancer. The types of cancer listed below are the common ones.


Leukemia:

Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts."

Leukemia is a broad term covering a spectrum of diseases. In turn, it is part of the even broader group of diseases affecting the blood, bone marrow, and lymphoid system, which are all known as hematological neoplasms.

Clinically and pathologically, leukemia is subdivided into a variety of large groups. The first division is between its acute and chronic forms:

• Acute leukemia is characterized by a rapid increase in the number of immature blood cells. Crowding due to such cells makes the bone marrow unable to produce healthy blood cells.
Immediate treatment is required in acute leukemia due to the rapid progression and accumulation of the malignant cells, which then spill over into the bloodstream and spread to other organs of the body. Acute forms of leukemia are the most common forms of leukemia in children.
How cancerous cells are formed
stages of cancer cell formation-


• Chronic leukemia is characterized by the excessive build up of relatively mature, but still abnormal, white blood cells. Typically taking months or years to progress, the cells are produced at a much higher rate than normal, resulting in many abnormal white blood cells. Whereas acute leukemia must be treated immediately, chronic forms are sometimes monitored for some time before treatment to ensure maximum effectiveness of therapy. Chronic leukemia mostly occurs in older people, but can theoretically occur in any age group.


2. Carcinoma


Carcinoma is the medical term for the most common type of cancer occurring in humans. Put simply, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that generally arises from cells originating in the endodermal or ectodermal germ layer during embryogenesis. More specifically, a carcinoma is tumor tissue derived from putative epithelial cells whose genome has become altered or damaged to such an extent that the cells become transformed, and begin to exhibit abnormal malignant properties.
Frequent Organ Sites of Carcinoma
• Lung: Carcinoma comprises > 98% of all lung cancers.

• Breast: Nearly all breast cancers are ductal carcinoma.

• Prostate: The most common form of carcinoma of the prostate is adenocarcinoma.

• Colon and rectum: Nearly all malignancies of the colon and rectum are either adenocarcinoma or squamous cell carcinoma.

• Pancreas: Pancreatic carcinoma is almost always of the adenocarcinoma type and is highly lethal.
Some carcinomas are named for their or the putative cell of origin, (e.g. hepatocellular carcinoma, renal cell carcinoma).

CAUSES OF CANCER


It is very complex to study the causes of cancer. The causes of cancer can be explained genetically and clinically. The major cause of cancer is mutation of genes (proto oncogenes).

The substances that cause cancer are called carcinogens. A carcinogen may be a chemical substance, such as certain molecules in tobacco smoke. The cause of cancer may be environmental agents, viral or genetic factors.

We should bear in mind, though, that in the majority of cancer cases we cannot attribute the disease to a single cause.

We can roughly divide cancer risk factors into the following groups:

• biological or internal factors, such as age, gender, inherited genetic defects and skin type

• environmental exposure, for instance to radon and UV radiation, and fine particulate matter

• occupational risk factors, including carcinogens such as many chemicals, radioactive materials and asbestos

• lifestyle-related factors.

Lifestyle-related factors that cause cancer include:

Tobacco

Alcohol

UV radiation in sunlight

some food-related factors, such as nitrites and poly aromatic hydrocarbons generated by barbecuing food)

Cancer as a Multi-step Process

It is clearly known that cancer is caused by mutation. Cancer as a multi-step process explains that a single (one-time) mutation in gene is not enough to cause cancer. A single mutation in gene has only increased the tendency to have cancer. Various mutations of gene is what leads to formation of cancer cells.
This implies that as one ages, the tendency to be diagnosed of cancer increases. In summary of the above, cancer is age dependent. The process is stated below:
• After mutation of genes-controlling cell proliferation, a benign tumor is formed. The benign tumor can be easily removed by surgery.
• But when the cells metastasize ( move to other parts of the body) they now become Malignant tumor which becomes difficult to treat.




How Chromosomes Affect Cancer Cells



Chromosomes are thread like structures which are known to contain the genes and proteins. In the study of cancer cells, it was clearly stated that cancer is caused by the mutation of genes which are located in the chromosomes. This clearly shows how important chromosomes are in the study of cancer cells.

There are various ways chromosomes affect cancer cells. One of which is Chromosomal Rearrangements.

Chromosomal rearrangement as it name implies is the rearrangement of chromosomes wrongly which causes mutations of gene. An example is in Leukemia cells, the chromosome 9 moves to chromosome 22.



This disorder causes cancer in the affected patient.

Controlling Cell Proliferation in Cancer Cells


Cell Proliferation is the abnormal increase in the number of cells. The Tumor Suppressor Gene controls the proliferation of cells. It prevents the formation of cancer cells and the spread by controlling the rapid growth of the cell.
Chemotherapy
This is a kind of treatment that uses drugs to attack cancer cells. It is called a "systemic treatment" since the drug, entering through the blood stream, travels throughout the body and kills cancer cells at their sites. Chemotherapy, often shortened to just "chemo". The drugs may rarely be intended to have a local effect, but in most cases, the intention is to destroy cancer cells wherever they may exist in the body.
  • Chemotherapeutic drugs are chemically designed to target cells that are dividing and growing rapidly. Once they reach the cancer cells, they act to retard their growth, eventually resulting in their destruction.
  • Chemotherapy may be given at home, in a clinic or in a hospital. The frequency of chemotherapy can be daily, weekly, monthly or an on-off schedule depending on the type of drug, the body's response and the type of cancer. The chemotherapy is decided on the basis of the type of cancer. The dosage is calculated on the basis of the patient's body weight and the drug's toxicity.
  •  The chemotherapy is concerned with the whole body.

Chemotherapy is used to treat:


• Early-stage invasive breast cancer to get rid of any cancer cells that may be left behind after surgery and to reduce the risk of the cancer coming back

• Advanced-stage breast cancer to destroy or damage the cancer cells as much as possible
--- In some cases, chemotherapy is given before surgery to shrink the cancer.
---At present more than 50 anticancer drugs have been discovered. They are used in several ways:

• Monotherapy or only one drug

• Combination chemotherapy or a group of drugs which work together

• Combined modality or chemotherapy along with other treatment such as surgery and radiotherapy
 The drugs are delivered to the affected cells in the following forms:

• Oral (tablet form, by mouth)

• Intravenous or Intramuscular (injected by needle into a vein or muscle)

• Intrathecal chemotherapy (injected through a needle in the back)


PREVENTION OF CANCER

1. Avoid the use of Tobacco
Tobacco is known to contain chemicals that promotes mutation of genes that causes cancer. Using any types of tobacco puts you on a collision course with cancer. Smoking has been linked to various types of cancer including lung cancer.
2. Eat a healthydiet
3. Protect yourself from the sun.



WHAT NEXT?

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References
Robert J. Brooker Concepts of Genetics
Leonard H. Hartwell and Leroy Hood Genetic- From Genes to Genomes
NPTEL – Chemistry – Bio-Organic Chemistry of Natural Enediyne Anticancer Antibiotics
Bhairab N. Singh Cell Proliferation https://www.nature.com/subjects/cell-proliferation


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