What is Cancer?

Cancer is a complex disease involving many types of cells. It starts when cells grow, make copies (reproduce), and spread in an uncontrolled way. This process can lead to the formation of a mass of cells called a tumor. Cancer can also spread to other parts of the body through the blood or lymphatic system. These new areas of cancer may be benign, or they can cause health problems by growing into tissues and organs. Cancer is one of the most common diseases in the United States. It affects people of all ages, races, and genders.

Most current general definitions of cancer describe what cancer “looks like” or “does” but do not adequately capture the dynamic processes that underlie the disease. For example, most cancers start when healthy genes get changed over time. These changes, which are sometimes passed down from parents to their children, can make a cell divide more often than it should or make the cells survive when they should die. These mutations can allow the cancer cells to spread and eventually destroy the entire body.

As with other populations of organisms, cancer cells adapt to their microenvironments as they evolve. As a result, different subpopulations of cancer cells can develop distinct phenotypes. These phenotypes allow cancer cells to better exploit the resources of the tumor microenvironment, co-opt normal cells for their benefit, and evade therapeutic mechanisms. These adaptations can contribute to the emergence of drug resistance.

The most common type of cancer is skin cancer, which often can be prevented by staying out of the sun and wearing protective clothing when needed. Regular screening tests can find cancers at an early stage when they are easier to treat. These screening tests include colonoscopies, mammograms, and Pap smears. Vaccines can also help prevent some cancers. For example, the human papillomavirus (HPV) vaccine helps prevent most cases of cervical cancer.

Many types of treatment can cure or control cancer, but the best treatments depend on the kind and stage of your cancer. Your doctor can tell you about the benefits and risks of each treatment.