What causes cancers to occur?

Sakeena Bajwa

Cancer is defined as a disease which is caused by the abnormal cells which undergo uncontrolled division, in such a way that they become able to infiltrate and harm the healthy tissues of the body. Cancers are thought to start when changes occur in the genes that control cell division.

The underlying cause of cancer cell formation is DNA mutation (change in genes).

The mutated gene that causes cancer is called oncogene, after the Greek word “onkos” meaning bulk or mass. But, mutation is not always harmful, most of the times mutated cells are too weak to survive for longer or they are destroyed by the immune system.

The cancerous cells show particular biological capabilities which distinguish them from normal cells, we call these properties the hallmarks of cancer. The prominent hallmarks of cancer are:

1.     Sustaining growth signalling

The receptors of growth factors present on the surface of the cell attaches a growth factor from neighbouring cells. This initiates a signalling cascade inside the cell which leads to cell growth and division. Normally, the cells start dividing after receiving the growth signal from other cells and undergo division in a coordinated manner.

On the contrary, cancerous cells do not need growth signals from outside and continue to divide on their own. Due to this intracellular signalling cascade the mutations are passed on to the daughter cells causing proliferation of the cancerous cells ultimately forming a tumour. Typically, a tumour contains a thousand million cancerous cells.

Cancer cell or cancerous tumor amidst flowing red blood cells in a blood vessel, artery or vein 3D rendering illustration. (Source: istockphoto, Unsplash)

2.     Insensitivity to growth suppressors

The cells usually tend to maintain the homeostatic state that’s why, growth suppressors are also present in the cells along with the growth factors to keep a balance in cell growth. The cancerous cells do not respond to these antigrowth signals from other cells and continue to grow in uncontrolled way.

The insensitivity of cancerous cells to the growth suppressors also leads to the proliferation of these mutated cells. The mutations inactivate the tumour suppressing genes p53, RB1 and TGF-β in the cancerous cells so there’s no one to stop them from making a bulk or tumour.

3.    Evading cell death

The 3rd hallmark of cancer is the resistance of cancerous cells to cell death. For non-cancerous cells, the mutated cells receive the apoptosis signal from within and die themselves. Cancerous cells do not undergo this phenomenon due to mutation in signalling protein hence, they evade cell death and keep dividing giving rise to new cancer cells like them. 

4.     Immortal potential of replication

Cancerous cells overcome the property of ‘dying naturally after the fixed life span of cell’ which happens in normal cells. They become immortal and get never-ending replicative strength due to the addition of extra telomeres in the chromosomes of mutated cells. That’s why, all cells in a tumour remain alive and keep consuming energy ultimately weakens the body.

5.     Ability to sustain angiogenesis

Cancerous cells secrete the vascular endothelial growth factors and basic fibroblast growth factors (VEGF and bFGF). that induce the proliferation pf blood vessels hence provide nutrients and oxygen to the tumour cells. This phenomenon of blood vessel growth is known as angiogenesis which is a vital process in growth and development (as that in wound healing).

6.     Metastasis/tissue invasion

The 6th hallmark is the most dangerous one i.e. metastasis. The cancerous cells are capable of invading and damaging the surrounding tissues and sometimes, they not only attack the tissues present around them but also move from one part of body to the other through blood.

This happes when cell adhesion is broken, extracellular matrix is degraded and chemotaxis brings motility to the tumour. After this, tumours begin to form in other parts of the body as well.

Other hallmarks:

There are some other properties of cancerous cells like:

Avoiding Immune Destruction

There rises another question i.e. why the cancerous cells aren’t destroyed and phagocytosed by immune system? Our immune system can destroy small tumours but, when the tumours grow fast and become large and solid, they resist the action of immune system and evade destruction. 

Chances of Cancer are more in individuals with weak immune system due to some immunity disorder as in HIV and attack of tumour viruses.

Unstable genome

Cancerous cells have instability in genome and continuous mutations make them more complicated.

Alteration in /energetics

Cellular energetics in cancerous cells is deregulated, lesser efficiency in glycolysis and synthesis of some amino acid precursors make them abnormal.

 Role of inflammation

Some inflammations due to infections in the cells secrete tumour promoting chemicals and ultimately cause cancer.

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