Cancer is not one disease, but a collection of related diseases that can occur almost anywhere in the body. At its most basic, cancer is a disease of the genes in the cells of our body.
Genes control the way our cells work. But, changes to these genes can cause cells to malfunction, causing them to grow and divide when they should not—or preventing them from dying when they should. These abnormal cells can become cancer.
Understanding how genetic changes cause cancer is one way to understand this disease, while cancer statistics is another. Cancer statistics help scientists understand the burden of cancer on society.
Statistics can tell us things such as how many people are diagnosed with and die from cancer each year and the number of people who are living after a cancer diagnosis. Changes in statistics over time can help scientists find areas where progress is needed.
Cancer statistics also help scientists understand cancer health disparities. Examples of disparities include the higher cancer death rates, less frequent use of proven screening tests, and higher rates of advanced cancer diagnoses that are found in certain groups of people.
What Is 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 tumours.
Many cancers form solid tumours, which are masses of tissue. Cancers of the blood, such as leukaemias, generally do not form solid tumours.
Cancerous tumours are malignant, which means they can spread into, or invade nearby tissues. In addition, as these tumours 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 tumours far from the original tumour.
Unlike malignant tumours, benign tumours do not spread into, or invade nearby tissues.
Benign tumours can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumours sometimes do.
Unlike most benign tumours elsewhere in the body, benign brain tumours can be life-threatening.
Cancer Cells Vs Normal Cells
Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive.
One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not.
This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.
In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells.
Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumour—an area known as the microenvironment.
For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumours with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumours.
Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions.
Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system.
Tumours can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.
How Cancer Arises?
Cancer is caused by certain changes to genes, the basic physical units of inheritance. Genes are arranged in long strands of tightly packed DNA called chromosomes.
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.
Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun. (Our Cancer Causes and Prevention section has more information.)
Each person’s cancer has a unique combination of genetic changes. As cancer continues to grow, additional changes will occur. Even within the same tumour, different cells may have different genetic changes.
In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may have nothing to do with cancer; they may be the result of cancer, rather than its cause.
When Cancer Spreads
In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumours (metastatic tumours) in other parts of the body. The metastatic tumour is the same type of cancer as the primary tumour.
Cancer that has spread from the place where it first started to another place in the body is called metastatic cancer.
The process by which cancer cells spread to other parts of the body is called metastasis.
Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer. For example, breast cancer that spreads to and forms a metastatic tumour in the lung is metastatic breast cancer, not lung cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of original cancer. Moreover, metastatic cancer cells and cells of original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
Treatment may help prolong the lives of some people with metastatic cancer.
In general, though, the primary goal of treatments for metastatic cancer is to control the growth of cancer or to relieve symptoms caused by it.
Metastatic tumours can cause severe damage to how the body functions and most people who die of cancer die of metastatic disease.
Cancer treatment aims to remove tumors or limit their growth
- There are many different types of cancer treatment. All of them aim to remove the malignant tumour, or at least limit how much cancer can grow and spread.
- Some cancers can be removed by surgery. Medication (chemotherapy) or various types of radiotherapy are sometimes used to shrink tumours before surgery.
- These treatments might be used after surgery too, to destroy any cancer cells that are left and prevent cancer from growing back (recurrence).
- Chemotherapy and/or radiotherapy are still options even if the tumour can’t be removed by surgery.
- The exact treatment will depend on various things, like the type of tumour and the stage of the disease.
- Medications known as cytostatic drugs are typically used in chemotherapy. These drugs can kill cancer cells or make sure that they don’t continue to grow.
- Other medications prevent the development of new blood vessels that feed the tumour. That can slow the growth of the tumour.
Development and Elimination of Cancer Cells
- Some drugs interfere with the cancer growth process by reducing the effect of hormones and other chemical messengers on the cells.
- Nowadays there are also medications that can boost the immune system‘s ability to fight off certain types of cancer cells.
- Researchers are always looking for new ways to limit the growth and spread of cancer cells.
This article has been taken from the National Cancer Institute of U.S. Department of Health and Human Services.
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