What Is Cancer and How it Spreads

Cancer is a disease in which certain cells in the body grow uncontrollably and spread to other parts of the body.

Cancer can develop almost anywhere in the human body, which contains trillions of cells. Human cells normally grow and multiply (a process known as cell division) to form new cells as the body requires them. Cells die when they become old or damaged, and new cells replace them.

When this orderly process fails, abnormal or damaged cells grow and multiply when they should not. These cells can combine to form tumors, which are tissue lumps. Tumors may or may not be cancerous (benign).

Cancerous tumors invade nearby tissues and can travel to distant locations in the body to form new tumors (a process called metastasis). Cancerous tumors are also known as malignant tumors. Many cancers form solid tumors, but blood cancers, such as leukemias, do not.

Benign tumors do not invade or spread into nearby tissues. When benign tumours are removed, they usually do not recur, whereas cancerous tumours occasionally do. However, benign tumors can grow to be quite large at times. Some, such as benign brain tumors, can cause serious or fatal symptoms.

The Differences Between Cancer and Normal Cells

Cancer cells are distinct from normal cells in numerous ways. Consider cancer cells:

• Grow in the absence of signals instructing them to do such Normal cells only grow in response to such signals.

• Disregard signals that normally tell cells to stop dividing or die (a process known as programmed cell death or apoptosis).

• Invade surrounding areas and spread to other parts of the body Normal cells stop growing when they come into contact with other cells, and most normal cells do not move around the body.

• Instructing blood vessels to grow toward tumors These blood vessels deliver oxygen and nutrients to tumors while also removing waste.

• Instructing blood vessels to grow toward tumors These blood vessels deliver oxygen and nutrients to tumors while also removing waste.

• Evade the immune system Normally; the immune system eliminates damaged or abnormal cells.

• Trick the immune system into assisting cancer cells in their survival and growth Some cancer cells, for example, persuade immune cells to protect the tumor rather than attack it.

• Accumulate multiple changes in their chromosomes, such as chromosome duplications and deletions Some cancer cells have twice as many chromosomes as normal.

• Rely on different types of nutrients than healthy cells Furthermore, some cancer cells generate energy from nutrients differently than most normal cells. This allows cancer cells to grow faster.

Cancer cells frequently rely so heavily on abnormal behaviors that they cannot survive without them. Researchers have capitalized on this by developing therapies targeting cancer cells' abnormal characteristics. Some cancer therapies, for example, prevent blood vessels from growing toward tumors, effectively starving the tumor of nutrients.

How does cancer develop?

Cancer is a genetic disease, which means that it is caused by changes in the genes that control how our cells function, particularly how they grow and divide.

Cancer-causing genetic changes can occur as a result of the following:

• Of errors that occur during cell division

• DNA damage is caused by harmful environmental substances such as tobacco smoke chemicals and ultraviolet rays from the sun (For more information, see our Cancer Causes and Prevention section.)

• They were passed down from our parents.

Normally, the body eliminates cells with damaged DNA before they become cancerous. However, our bodies ability to do so declines as we age. This contributes to the increased risk of cancer later in life.

Each person's cancer has a distinct set of genetic changes. Additional changes will occur as cancer progresses. Different cells within the same tumor may have different genetic changes.

Types of Cancer-Causing Genes

Cancer-causing genetic changes primarily affect three types of genes: proto-oncogenes, tumor suppressor genes, and DNA repair genes. These changes are sometimes referred to as cancer "drivers."

Proto-oncogenes play an important role in normal cell growth and division. When these genes are altered or become more active than usual, they can become cancer-causing genes (or oncogenes), allowing cells to grow and survive when they should not.

Tumor suppressor genes are also involved in cell growth and division control. Cells with certain mutations in tumor suppressor genes may divide erratically.

DNA repair genes are involved in the repair of damaged DNA. Cells with these genes are more likely to develop additional mutations in other genes and chromosomal changes, such as chromosome duplications and deletions. These mutations, when combined, may cause the cells to become cancerous.

Scientists have discovered that certain mutations commonly occur in many types of cancer as they have learned more about the molecular changes that lead to cancer. Many cancer treatments are now available that target gene mutations found in cancer. A few of these treatments are available to anyone with the targeted mutation, regardless of where the cancer began to grow.

When Cancer Spreads

Metastatic cancer is cancer that has spread from the site of origin to another part of the body. Metastasis is the process by which cancer cells spread to other parts of the body.

Metastatic cancer has the same name as primary cancer and the same type of cancer cells. For example, breast cancer that has spread to the lungs is called metastatic breast cancer rather than lung cancer.

Under a microscope, metastatic cancer cells resemble cells from original cancer. Furthermore, metastatic cancer cells and original cancer cells usually share some molecular characteristics, such as the presence of specific chromosome changes.

Treatment may help people with metastatic cancer live longer lives in some cases. In other cases, the primary goal of treatment for metastatic cancer is to control cancer's growth or to alleviate the symptoms it causes. Metastatic tumors can severely impair how the body functions, and metastatic disease kills most cancer patients.