Friday explainer: What is cancer?


What is cancer?
Cancer is a blanket term for more than 100 related diseases that have a core characteristic in common—unchecked cell growth.

At the most basic level, cancers occur when cells divide out of control, eventually interfering with important processes that keep us healthy. Cancer cells also may spread to other tissues, a process called metastasis.

Cancer cells have an arsenal of tools to help them spread. They can hide from the immune cells that make up the body’s defense system. They can cause the other cells around the tumor, called the tumor microenvironment, to reroute resources to supply the tumor with needed nutrients. And, because they are less specialized, cancer cells can divide endlessly, unlike healthy cells, which can divide only a limited number of times.

What causes cancer?
Our bodies are made up of an estimated 37.2 trillion cells, each of which has a particular job and usually operates on a set life cycle. Normally when a cell grows old or becomes damaged, it dies, which makes room for new cells. In cancer, old or abnormal cells survive and continue to divide. They may then form masses of tissue called tumors.

But what goes wrong? How does a normal cell become a cancer cell?

The answer lies in the instructions that make us human—our genetic code. Ultimately, cancer is the result of errors in these instructions or in the way they are read and acted upon. There are many ways that this can occur, including:

  • Mistakes in DNA replication: During the normal cell division process, our genetic code is copied and passed on to new cells. Occasionally, mistakes occur and the code is copied incorrectly. These errors are usually fixed by a cell’s quality control process, but sometimes errors do slip through the cracks. Cancer can arise when these errors occur on certain genes, such as those that tell cells when to stop dividing.
  • Genetic inheritance: Some genetic mutations that increase cancer risk may be passed down from generation to generation. An example is mutations to the BRCA1 and BRCA2 genes, which increase the risk of developing breast and ovarian cancer.
  • External factors: Many things can cause DNA mutations that may eventually give rise to cancer. Examples include sunlight (skin cancers); viruses, such as certain strains of human papilloma virus (cervical cancer), and bacteria such as Helicobacter pylori (stomach cancer); substances such as asbestos (mesothelioma); and lifestyle choices, such as smoking cigarettes (lung, throat, and oral cancers).

How does research impact cancer treatment?
Understanding how cancer works on a basic level allows scientists to develop new ways to more precisely treat it. Here are some examples of areas that are at the forefront of cancer research.

  • Personalized medicine: No two people are the same and no two cancers are the same. Using cutting-edge techniques to understand an individual’s specific disease helps physicians to tailor treatments that better fit the patient.
  • Epigenetic therapy: Sometimes it’s not a change in the genetic code that causes a problem but rather an error in the way the code is read. Drugs that target these epigenetic errors—errors literally “on top of” the genome—have in some cases been shown to “prime” cancer cells, making them more receptive to other therapies. This growing area of research holds great promise for finding new ways to treat cancer.
  • Immunotherapy: Immunotherapies harness the robust strength of the body’s natural defenses to fight cancer. In 2013, the prestigious journal Science named immunotherapy as the Breakthrough of the Year, highlighting clinical successes as well as the work of immunotherapy pioneer Dr. James Allison.


Gene: Chunks of DNA that contain the instructions for a particular trait or function. (Check out a list of genes and their functions here)

Genetic mutation: A permanent change to the DNA sequence that can affect one gene or many. Some mutations can be passed down through families while others occur during a person’s life and cannot be passed down. (Read more here)

Epigenetics: Literally meaning “on top of genetics”, epigenetics are a set of controls that tell our genes when to switch on or off. When epigenetic mechanisms go awry, the instructions can be read incorrectly, leading to diseases such as cancer. (Read more here)

Cell: The basic building block of all living organisms. (Read more here)