top of page
  • Vann

What makes cells cancerous?

By Thomas Broom, Vann and Oxford University

Image by Dennis,

Cancer occurs when some cells in the body begin to grow and replicate uncontrollably (1), (2). The key to understanding how cancer develops is to take a closer look at what goes on inside our cells. What are the changes inside our cells that can lead to cancer? What makes cancer cells different?

The origins of cancer cells

Scientists estimate that the average human is made up of around 30 trillion cells (3). Normally, all these cells exist in a complex balance – dividing, dying and being replaced in a healthy, controlled way so that we always have the right number of each type of cell (3), (4). Cells normally only divide to make more cells when they are told to, and die when they become old or damaged (1).

Cancer can begin when something goes wrong in a cell, and it starts ignoring this balance. The cell might keep dividing when it shouldn’t. It might start ignoring the normal signals that tell it to be replaced by new, healthy cells. As this cell replicates it can form a larger collection of cells called a tumour (5). During their continued growth, the cancer cells may also move to parts of the body where they shouldn’t be and cause harm (6).

What changes in a cancer cell to make it behave like this?

It's all in the DNA...

Every cell in the body contains DNA, the molecule that carries the instructions for everything the cell does. The instructions in the DNA are organised into ‘genes’ – sections of DNA that each control a particular aspect of how the cell behaves.

Lots of genes are involved in how the cell grows and divides (7). Normally, these genes will make sure the cell only divides when it should. However, genes can change in a process called mutation. Mutation often happens by chance when normal cells divide and small mistakes are made when the DNA is copied4. Mutations can also be inherited from our parents, or can arise after exposure to harmful carcinogens that can damage the DNA (1).

When a gene mutates it can stop working or work in a different way to how it should. Mutations in the genes involved in cell growth can cause the cell to start dividing out of control, leading to cancer.

For example, there are a group of genes called tumour suppressor genes, which are genes that slow down cell division and instruct cells to die if they need to be replaced (7). They help to maintain that important balance of cell growth and replacement in the body. If mutations arise in a tumour suppressor gene, it may stop working properly, and will no longer be able to keep cell division in check, potentially leading to the cell dividing uncontrollably and becoming cancerous (3).


Cancer begins when a cell in the body acquires a genetic mutation or change that causes it to begin growing and dividing uncontrollably. The cell ignores the normal signals telling it to stop replicating or to be replaced and begins to form a mass of cells that can develop into a tumour.


1. National Cancer Institute, 2021. What Is Cancer?. Available at: [Accessed March 2023]

2. Cancer Research UK, What is cancer?. Available at: [Accessed March 2023].

3. Weinberg, R. A., 1996. How Cancer Arises. Scientific American, September, pp. 62-70.

4. Eldridge, L., 2022. Cancer Cells vs Normal Cells: How Are They Different?. Available at: [Accessed March 2023].

5. Cancer Research UK, How cancer starts. Available at: [Accessed March 2023].

6. National Cancer Institute, Cell Biology of Cancer. Available at: [Accessed March 2023].

7. American Cancer Society, 2022. Genes and Cancer: Oncogenes, Tumor Suppressor Genes, and DNA Repair Genes. Available at:

[Accessed March 2023].

14 views0 comments
bottom of page