[-Saturday, January 20, 2007-]

Wad is Cancer?

Wad is Cancer?

Cancers are tumour cells which are able to invade neighbouring cells and eventually metastasize (Terminal stage).

Tumours cells are cells which proliferate in an unappropriate manner which cannot be controlled. These tumour cells are undifferentiated. So they are of no use to the body. Normal cells will undergo differentiation to specific function cells such as nerve cells or muscle cells.

Tumours cells are common to everyone. Mutation occurs randomly and causes the mutated cells to start cell division unappropriately causing tumour cells. We may or may not be able to feel the tumours. However, most of the tumours are harmless. Nutrients, oxygen and waste products diffused from our blood stream to enable the survival of these tumours. If the tumour grows too big and the rate of diffusion is unable to facilitate such processes, the tumour cells will undergo Apoptosis aka Cell Death for the good of the rest of the cells.

However, if the tumour is able to conduct angiogenesis (growth of blood vessels on the tumour), the tumour will grow rapidly and to a larger size at a much faster rate. This is still not cancer.

The stage where it is known as the malignant tumour (cancer) is when they start to invade the neighbouring cells. This stage is mostly curable as a surgery is sufficient to remove the affected part. However, the terminal stage (metastasis) where the cancer cells start to break away and move to other parts of the body via our blood transport system. There will be no possibilty of cure.

So wad causes cancer?
Cancer are caused mostly by mutation and lifestyle and is a inheritable disease. Why?

Why cancer are caused by mutation?
Studies are performed by mutation of genetic DNA. 3 classes of DNA are especially closely connected to the cause of cancer.

1. DNA repair genes
2. Oncogenes
3. Tumour Suppressor genes

DNA repair genes are genes that expressed proteins that helped to repair DNA which are damaged due to mutations. If a DNA is damaged and the cells are unable to repair the genes, the cell with the damaged DNA will undergo programmed Cell Death (Apoptosis) to prevent further problems to the rest of the cells.

Oncogenes are genes that expressed growth signals for the cells to undergo cell division appropriately. 1 cell undergoes cell divide to give 2 daughter cells. Den these 2 cells will undergo cell division to give 4 daughter cells etc.. If an oncogene is mutated, it will cause the cells to undergo cell division unappropriately, giving rise to undifferentiated tumour cells.

Tumour Suppressor genes are genes that suppressed Tumour. If it is mutated, tumour cells will be allowed to grow.

Therefore, DNA repair genes are impt. If it is mutated, mutated Oncogene and T. Suppressor gene will not be repaired.. Thus, allowing tumour cells to proliferate.

Further studies had shown that mutation takes time to occur as several mutation of various T. Suppressor genes are required before they are rendered helpless in stopping formation of tumours. Therefore, lung disease due to smoking took 10-20 years to take effect. During these 10-20 years, mutation occured randomly within your body. With smoking, you are only hastening the rate of mutation together with Mr Probability.

Why cancer is an inheritable disease?
Studies had proven that this is indeed an inheritable disease.

1. When a DNA gene in a cell is mutated causing cancer cell. When the cancer cell divide, both 2 daughter cells consist the same DNA gene with the same affected region.

To put in simple words, they are the exact replica of the cancer cell. In a normal cell wen undergoing cell division, the 2 daughter cells are not exact replica of the parent cell. Some traits changes during mitosis. This does not apply to cancer cells however.

2. For woman germline cells which consist of XX chromosomes. 1 X chromosome will be inactivated as Barr Bodies. Which X chromosome to be inactivated is random for normal cells. However, for the cancer cell, if the paternal X chromosome is inactivated, the daughter cells of the cancer cell will also hab their paternal X chromosomes being inactivated.

Oncogenes
As mentioned earlier, Oncogenes are genes that promote expression of growth signals which signal the initaition of cell division in a controlled manner. However, if Oncogenes were to be mutated, it may signal cell division to occur inappropriately, that is cell division occurs repeatedly for the cells, forming tumour.

I will discuss on a Oncogene which is called the Ras. Ras and Myc are both linked to cancer.

Ras activates a cascade of pathways which involve Myc, PKB, E2F, p53. p53 is especially impt as it initiates Cell Death when activated. One reason why cancer is prevalent is bcos the pathway linking to cell death is obstructed, meaning p53 is being inactivated.

Ras
Ras leads to 2 pathways. 1 pathway leads to Cell Division or Cell Growth and Cell death as well via Myc and E2F. U may wonder how come it leads to both cell growth and cell death at the same time.

Rem this: What goes in must = What comes out. Life is in an equilibrium state. If this equilibrium is disrupted, trouble looms ahead.

1 pathway leads to inhibition of Cell Death via PKB.

Therefore, if Ras is mutated to be able to over expressed in our body. The signal to inhibition of Cell Death and initiation of Cell Growth both increased. Hence, tumour will be formed. Experimental studies of mice with mutated overexpressed Ras results in the mice having breast tumour.

Myc
Unlike Ras, Myc is activated by Ras and in turn only lead to the pathway which leads to Cell Growth and Cell Death. Therefore, if Myc is mutated to be overexpressed. The signal to Cell Growth and Cell Death increased hence no tumour is found in the mice with mutated Myc.

Ras + Myc Wad will happen?
If a mice with both mutated overexpression of Ras and Myc genes, tumour occured at a faster rate. As both Ras and Myc both signal to Cell Growth and furthermore, Ras signals the inhibition of Cell Death. Therefore, the tumour cells will only increase and not decrease.

This expt further proves that more than a single mutation is needed for cancer to occur.
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