Death is a constant factor in our lives. It is the undeniable truth in the inevitable cycle of life. The LIFE EXPECTANCY, which is the average time a human is expected to live, has enhanced over the last few decades. A hundred years ago, humans did not live for exceptionally long – men were expected to live till the age of 58.8 and women till the age of 60.6 between the years of 1920 – 1922. As medical technologies advanced, so did the life expectancy of humans. Currently, the life expectancy for both the sexes has increased by more than 10 years. This addition of an entire decade is a boon to mankind, but the burden of death remains.
As humans thought they had conquered death by adding more years in the bank of their life, numerous problems also came to light. With lifestyle changes came conditions which – although curable – could diminish the quality of life for the person. As medical science excelled, the instances of heart disease, diabetes and cancer and their corresponding death toll were observed. Instantly, research in these fields began and these have become the largest funded research projects worldwide. Unfortunately, these are also some of the leading causes of death.
The word ‘cancer’ has also become exceedingly popular, thus making people aware of the repercussions of the fatal disease. Although newer drugs and therapies are being researched upon, the impending doom of cancer remains. A World Health Organisation statistic reveals that in 2012, there were 14.1 million cases of cancer, with the death toll being 8.2 million – this statistic suggests that more than 50% of the cancer patients meet an unfortunate end.
Nearly every biologist is encouraged to join the fight against cancer and several do. The work of each scientist spending countless hours in the laboratory, every doctor and nurse tirelessly tending to their patients and the millions of people having their lives uprooted due to cancer have a role in this fight. The initial step to partake in this movement is to understand cancer. Superficially, cancer is caused due to the overgrowth of cells in the body – which may be downplayed often, but one must remember that it can end lives and permanently tarnish that of several others.
What is the mechanism of proliferation of cancer cells?
Numerous theories explain the growth of cancer cells, the understanding of which would require an acute comprehension of cell biology and genetics. Cancer is caused due to UNCONTROLLED growth of cells, which often invade functional cells and deny them of their cellular function. CANCER BIOLOGY or ONCOLOGY is the field dedicated to understanding the mechanism of cancer and it involves several other fractions of the field which collaborate with genetics, epigenetics, and cell biology. However, the basic theories concerning cancer will be outlined below.
Everyone harbour a set of genes on their genetic material (DNA) called oncogenes. Oncogenes are genes which facilitate the onset of cancer and promote the proliferation of cancer cells. Oncogenes must be TRIGGERED to made active – which can be done by CARCINOGENS. Carcinogens may be forms of radiations, chemicals, or viruses. When the oncogenes are rendered active, the whole cycle of cancer is initiated.
- Evasion of the cell cycle
The cell cycle (which is MITOSIS for SOMATIC CELLS and MEIOSIS for GERM CELLS) can be aptly described as the life cycle of a cell, which primarily aims at the division of a cell. Every cell in the body must adhere to its cell cycle – which is an extremely detailed and strict protocol – to appropriately carry out its functions. It is so delicate that it has CHECKPOINTS serially. The cell cycle checkpoints are biomolecules which ensure the cell is at the correct stage in the cycle. Failure of the cell to pass at the checkpoints indicates a malfunction in the cell.
Once the oncogenes of a cell are activated, the cell evades the cell cycle. The checkpoints are rendered useless and the cell – without a regulatory mechanism in place – proliferates uncontrollably. This leads to several cells which share the same characteristics of the original cancer cell. If cancer cells spread from one location to another, it is called METASTASIS.
3. Prevention of APOPTOSIS
Apoptosis is perhaps one of the most essential functions of a cell – its death. A living body must maintain the cycle of apoptosis and regeneration of the cells to ensure HOMEOSTASIS. Apoptosis is scientifically defined as PROGRAMMED CELL DEATH. When a cancer cell evades the cell cycle, it loses its characteristic of apoptosis. Apoptosis is a function of the cell cycle checkpoints and the absence of those inhibits the process of apoptosis as well.
Apoptosis is also defined in terms of genetics – the ends of the DNA strands (TELOMERES) in a cell are non-conservative, i.e., they shorten in length with subsequent cell divisions. Once a cell loses a big chunk of DNA, it is unable to perform its functions and apoptosis is triggered. Cancer cells do not show the property of telomeric shortening and thus are essentially immortal.
4. CONTACT INHIBITION
Contact inhibition is a property of a cell which has been extensively studied in ANIMAL TISSUE CULTURE. It is a characteristic by which cells stop their proliferation once they encounter another cell of the same kind. It is a regulatory procedure which prevents cells from overlapping and ensuring they grow in a MONOLAYER – this property is also expressed in vitro.
Cancer cells are ignorant to contact inhibition as they lose the ability to trigger the appropriate molecules required to signal an encounter with another cell. Thus, cancer cells – now unregulated by the cell cycle, the property of contact inhibition and being immortal – pile upon one another, regardless of whether the cells are oncogenic or not. The accumulation of cells gives rise to a TUMOUR. If the cancer cells overlay on functioning cells, these cells are unable to process their functions and undergo apoptosis. Thus, the oncogenes may initiate at a certain location, but migrate to the different parts of the body by invading the functional cells.
What are the causes of cancer?
Cancer are of several types and can affect nearly all parts of our body. Since the spread of cancer is ambiguous, there are no set causes which can lead to cancer. A healthy person who is not even in the reach of a carcinogen may be detected of cancer. However, there are certain common causes of cancer. Largely, the reasons for cancer are CARCINOGENS, which activate the oncogenes, or MUTAGENS, which cause mutations in the genetic code.
- Lifestyle issues
The lifestyle of a person determines their life out in the world and many times even manifests in their body. Several cases of cancer have been reported and some lifestyle habits have found to be common in them. For instance, irresponsible consumption of alcohol can adversely affect the liver and can trigger the oncogenes of the HEPATOCYTES. Smoking is also a primary cause of lung cancer.
People working in the radiology department of the hospitals may be accidentally exposed to radiation – which is an important mutagen and carcinogen. Limiting the exposure to any sort of radiation is crucial to keep cancer at bay.
Certain viruses carry the property of being carcinogenic. Viruses can enter a cell and make the nucleus do its bidding, thereby causing a mutation in the genetic code. In this case, the mutations caused by the viruses are carcinogenic. One of the most prominent carcinogenic viruses is the HUMAN PAPILLOMA VIRUS (HPV) which directly invades the CERVICAL CELLS and causes cervical cancer.
A step towards scientific development was achieved with the introduction of the cervical cancer VACCINE – containing the attenuated HPV virus. This vaccine is recommended for women in the reproductive stage to reduce the chances of cervical cancer. Other viruses which can cause cancer are Helicobacter pyroli, Epstein-Barr virus and Hepatitis-B virus.
Various chemicals which are present in everyday essentials in small quantities are carcinogens and mutagens. These compounds may be present in shampoos and soaps of other kind and even food materials. While it is nearly impossible to check the effects of these chemicals in humans (since it is unethical to induce cancer in a human for research purposes), we must be aware of these compounds and act according to our discretion. Elements such as nickel and chromium, compounds such as asbestos and pesticides and plastics such as vinyl chloride have been deduced to possess carcinogenic properties.
4. Genetic predisposition
A well-known type of cancer which may have a genetic component to it is BREAST CANCER. Every human has two genes which prevent breast cancer – BRCA1 and BRCA2. These genes are involved in the repair of DNA which may cause tumours, thus termed as TUMOUR SUPPRESSING GENES.
0.25% of the population (i.e., 1 in 400) has a defect in one or both genes due to a genetic mutation. A mutation in these genes fails it to suppress tumours and hence, the chances of breast cancer are dramatically increased. A person carrying this gene can pass it on to their offspring and hence, breast cancer is often seen to run in the family. It is recommended for the children of breast cancer patients (especially daughters, although men can also develop breast cancer) to undergo a test to check whether their BRCA genes are also mutated. Often if the women are tested positive for the mutation, they are suggested to undergo a MASTECTOMY (removal of breast tissues) to reduce the occurrence of breast cancer.
Is cancer treatable?
The word ‘cure’ is seldom used in the context of cancer because one can never be certain that they have got rid of it. Hence, cancer is currently treated using a variety of techniques – such as CHEMOTHERAPY (administration of drugs which prevent the spread of cancer), RADIATION (subjection of the patient to powerful radiations to restrict the tumours) and SURGERY (to surgically remove the tumours which may have grown on the organs). Some cancers such as LIVER CANCER or LEUKEMIA are treated by transplant of the liver and bone marrow, respectively.
Every cancer patient who is aware of the cause behind their cancer sings a cautionary tale – one where the person must distance themselves from known carcinogens and addictions. Yet, there are thousands of people who suffer from the vague form of cancer – one which does not have a proven cause. Cancer is indeed one of those unexplainable miseries which can catch up to a person with little to no fault of their own.
However, the hope for curing cancer one day lies with the numerous scientists and doctors who work for uncountable hours to ensure no one must go through a journey like this. Advanced therapies and drugs are being proposed and worked upon every day and the work would not stop until the answer lies in front of us.