Figure: Cancer: A collection of related diseases
=> Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.
=> Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
=> When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors.
=> Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors.
=> Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.
=> Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening.
How cancer arises:
=> Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.
=> The development of a malignant tumor is undoubtedly inherited by some genetic mutation. These cancer causing mutations may occur in response to carcinogenic exposure, or failure of the body to repair its genetic mistakes.
Figure: Development of a malignant tumor
=> These mutations contribute to the increasing growth of tumors by either stimulating growth signals or failing to respond to stop signals. Protooncogenes will stimulate a cell to mature and divide, but when mutated they become oncogenes which can cause cells to divide endlessly. Conversly, mutations in the tumor suppresor genes will deny inhibition signals. Ultimately, a growth signal must travel to the interior of the cell to exert its effects. Inside the cell, transcription factors activate genes responsible for sending the cell through its cell cycle. One example is the mutated ras gene which encodes proteins that act continuously even when the receptors are not stimulating them. Such proteins are seen in approximately 1/4 of all human tumors.
=> Distress also occurs when tumor suppressors malfunction. Not only is the unbridled growth harmful, but the inability of the cell to stop this growth allows the forming tumor to metastasize. Mutations in inhibitory genes will allow the cell to ignore the inhibitory signal to halt growth.
=> The many checkpoints in the cell's growth cycle regulate the cell's growth. The binding of certain factors can cause a cell to be committed to progressing through the division cycle, and others may encourage resting. The factors can also encourage cell suicide in order to terminate damaged cells. When mutations occur in the genes encoding these factors, the result is a malfunction in the clock that regulates the cell cycle. This could include a failure to apoptose "sick" cells, or encouragement of a cell to continue into the division stage of the cell cycle when it should not be dividing. Failure of the body to eliminate genetically "sick" cells contributes to the malignancy by increasing the number of poor cells.
=> Immortality of cancer cells is caused by failure of the body to stop cell growth and eliminate cancer cells is what allows malignancies to grow out of control. One way cancer cells can become immortal is by the action of Telomerases which continuously replace the ends of chromosomes inhibiting chromosome breakdown. The normal action of telomerases allows "aging" of the chromosomes finally leading to death. Cancer cells often lack this enzyme allowing fresh capping to occur and continued life of that cell.
Figure: Enabling replicative immortality
=> Although malignancies take several decades to develop, some are noticed sooner than others. Inherited genetic mutation can cause malignancies to develop ong before carcinogenic substances can affect cells. Often carcinogenic exposure occurs to a localized cell or cells, wheras an inherited mutation is present in every cell once the zygote begins dividing.
Conclusion:
Cancer is unchecked cell growth. Mutations in genes can cause cancer by accelerating cell division rates or inhibiting normal controls on the system, such as cell cycle arrest or programmed cell death. As a mass of cancerous cells grows, it can develop into a tumor. Cancer cells can also invade neighboring tissues and sometimes even break off and travel to other parts of the body, leading to the formation of new tumors at those sites.
How Cancer Arises video:
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