October 2020
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The number of cells in a tissue is determined by the balance between cell division and cell death.

Uncontrollable cell division leads to the formation of abnormal growths called tumors. Tumors can be benign or malignant.

Benign Tumors

Benign tumors are slow-growing and constrained by surrounding connective tissue so they do NOT spread to other organs.

They can still be harmful or even kill by pressing on nearby nerves, blood vessels, or brain tissue. Examples of benign tumors include pituitary tumors which may press on optic nerves and cause loss of vision.

Malignant Tumors

Cancers are malignant tumors. These tumors can spread beyond the original organ where it comes from and to other organs of the body.

Cancer starts from damage in the DNA of a cell. This DNA damage is called MUTATION. Mutations happen when the cell duplicates its DNA prior to cell division and makes mistakes.

These damages are usually detected and repaired BEFORE the cell can divide. Sometimes, some of them may be ignored and transferred to daughter cells.

If the mutation is located in a gene that controls the cell cycle, it may affect the regulation of the cell cycle.

This could cause the cell to divide faster than it is supposed to.

Usually, one mutation is not enough to cause cancer. Cancer is usually the result of the accumulation of MANY mutations of genes involved in cell cycle control and DNA repair.

This commonly happens over a long period of time, over many rounds of cell divisions, and this explains why cancers are more common in older people.

Cancer Cells

Cancer cells do not stick together like normal cells. They move and invade nearby tissues and organs.

They may also spread to other organs by means of blood or lymph circulation.

Cancer cells from the original tumor, or primary cancer, can break out and may be taken up by a blood or a lymph vessel for a ride throughout the body.

They can then squeeze out from the vessel into other tissues and start a new tumor growth in the new location which will become secondary cancer.

While traveling in the bloodstream, a cancer cell usually stops at the first place where the vessel is getting so narrow that it gets stuck.

While traveling in the lymphatic system, cancer cells commonly get stuck in the nearest lymph nodes, where the vessels get narrower.

This is the reason why surgeons usually remove nearby lymph nodes when removing tumors.

The number of cells in a tissue is determined by the balance between cell division and cell death uncontrollable cell division leads to the formation of abnormal growths called tumors.

Tumors can be benign or malignant. Benign tumors are slow-growing and constrained by surrounding connective tissue so they do not spread to other organs.

They can still be harmful by pressing on nearby nerves, blood vessels, or brain tissue.

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