How Cancer Starts

Cancer is a disease that occurs when cells that normally control growth and division stop working properly. Instead, the cancer cells continue dividing and multiplying out of control. The growing cancer cells form a mass of abnormal cells called a tumor. The tumor can invade nearby tissue and spread to distant parts of the body through the blood or lymph system. Cancer is caused by changes (mutations) to genes. These mutations are usually caused by exposure to certain substances, such as tobacco smoke or ultraviolet radiation from the sun. Some mutations are inherited from parents, but most are acquired during a person’s lifetime.

The first step in understanding how cancer starts is to understand the basics of cell biology. Cells are the basic building blocks of all living organisms, from single-celled bacteria to multicellular animals like humans. Cells make up tissues, organs and other larger structures that provide the structural and functional basis of our bodies.

Most types of cancer begin when sections of DNA in the cells become mutated and start producing new cells that have altered properties. These mutations can be triggered by exposure to certain substances, such as chemicals in tobacco smoke or ultraviolet radiation from the sun. They can also be triggered by viruses that infect cells and cause them to produce mutations. Viruses that can trigger cancer include the human papillomavirus (which causes cervical cancer) and HIV (which causes acquired immune deficiency syndrome, or AIDS).

In normal multicellular organisms, most cells of a specific type are programmed to self-destruct after a set number of cell divisions. However, a few cell types, including stem cells that give rise to all other cell types, have the ability to continue dividing forever. Cancers arise when long runs of uncontrolled cell division occur, resulting in genetic mutations and an accumulation of oncogenic epigenetic changes.

These changes, or mutations, in the DNA allow cancer cells to reproduce faster and grow without normal controls. The mutations can also affect how a cell responds to signals that would normally trigger the cell to self-destruct or die. Cancer cells are able to grow and divide continuously, invade other tissues and promote the formation of blood vessels that supply them with nutrients.

Eventually, the cancerous cells accumulate in enough quantities that they outnumber healthy cells. These abnormal cells can then grow and divide without being stopped, forming tumors that can disrupt normal tissues and organ function. Cancer cells can also break away from the original cancer and travel through the blood or lymph systems to distant parts of the body, where they can form new tumors.

Many types of cancer can be cured if they are caught before the cancer spreads too far. However, some cancers can return after treatment. Researchers are constantly improving cancer treatments, and are developing more effective ways to prevent cancers from starting in the first place. The best way to prevent cancer is to have regular screening tests for the most common types of cancer, such as colon and cervical screening, or mammograms for breast cancer.