• Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

• Application: The correlation between smoking and incidence of cancers.

• Skill: Determination of a mitotic index from a micrograph.

• in the previous IB biology the cell cycle and mitosis article, we mention the cell cycle control and tumour 
• tumour is developed when the cell cycle is interrupted
• the cell keeps undergoing cell cycle, the excessive cells clump together. The clump of the cells is called tumour 

Tumour = the clump of the excessive cells due to the non-regular cell cycle

• 2 types of tumours which are benign and malignant 
• benign tumour: the tumour cells are confined to that area 
• malignant tumour: the tumour cells spread and grow in another area 

• the malignant tumour is cancerous 
• cancer starts when the primary malignant tumour migrates to other sites
• the tumour cells anchor and grow in a new place to form the secondary tumour, this process is called metastasis 

Metastasis = the spreading of cancer cells from the original area to other places within the bod

• cancer is not caused by a single reason, DNA mutation is one of the causes 
• Mutagens alter the DNA, it can be physical, chemical, or biological agents
  e.g. X-ray, UV light, chemicals in tobacco, aflatoxin in fungi, virus 
• if the mutagens are likely to induce cancer development, it is called carcinogen 

Mutagen = agents that alter DNA, not 100% is carcinogen
Carcinogen = the mutagens that cause cancer

• not all the mutation is caused by the mutagens, some time the DNA itself generates mutation, especially during the DNA replication, and we may acquire the mutation via inheritance 
• Usually, the DNA can repair the damage, however, but when the damage is too vicious or the DNA is repeatedly exposed to the mutagens, the damage cannot be healed and the DNA is mutated. 
• oncogene is the product of mutation 
• oncogene is the gene that likely to induce cancer 

Oncogene = genes with potential to cause cancer

• the precursor of the oncogene is the proto-oncogene. 
• proto-oncogene is a normal gene, it involves in the regulation of cell proliferation or inhibition of apoptosis (cell is programmed to die)
• It functions normally, causing no harm to our body, but once it is mutated, it becomes oncogene
• the oncogene boost up the cell proliferation and cause the cell that should undergo apoptosis to survive and divided instead --> cell clumps together --> tumour --> cancer 
• the oncogene becomes the target in the new cancer treatment 

• mutation is not 100% bad. In the IB biology chapter 1.5, we mention the cells in all the life in the Earth are derived from one ancestral cell. Mutation is vital to create the diversity of DNA sequences to give rise to different species, or else everything would be the same in the world (there won't be dog, cat, giraffe ....)
• Unfortunately, 99% of mutation is something bad. So.... if you hope you can be part of the X-Men by acquiring mutation, sorry it probably kills you first :(

• smoking is highly correlated to the bladder, cervix, kidney, larynx, stomach cancer 
• the risk of having lung cancer increases with the number of years of smoking and the number of cigarettes the person smokes 
• Quitting smoking can reduce the risk of having lung cancer 

• mitotic index is the ratio of cells undergo mitosis to the total number of cells
• it is a prognostic tool to review the efficiency of the cancer treatment, chemotherapy

mitotic index = the indicator of the efficiency of chemotherapy by counting the ratio of cells undergo mitosis to the total no. of cell

• low mitotic index = the treatment is efficient to cure cancer because, 
  low index number means the no. of cells undergo mitosis decreases --> decrease of cell undergoes cell proliferation --> the cancer size shrink 
• it is less accurate to the elderly because the mitosis in normal elderly is slow, so the index is low in healthy elderly 

In this IB Biology topic, you have to

1. understand the differences between benign tumour and malignant tumour (cancer)
2. understand the differences between mutagen and carcinogen 
3. known oncogene leads to cancer 
4. understand mutation is not 100% but still 99% bad 
5. remember LOW mitotic index means the chemotherapy is efficient 

That's the end of this topics

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Written by Queenie l IBDP Biology Specialist @ TUTTEE