The domino effect of mutations that turns cells into tumors

Science · Published 28 October 2026 Swipe more like this →

In short: Your body contains between 50 and 75 trillion cells, constantly dying and being replaced. Cancer begins when just one of these trillions malfunctions. It is not a sudden transformation but a cumulative failure of the genetic code, where small mistakes eventually bypass the body's repair systems to trigger uncontrolled growth.

The human body is a massive biological engine composed of 50 to 75 trillion cells. Under normal conditions, these cells follow a strict lifecycle of division and death. However, cancer emerges when a single cell begins to multiply excessively, forming a mass known as a tumor. The initial site of this abnormal growth is identified as the primary tumor, which can originate in almost any part of the human body.

At the heart of this process are genes—specific codes of DNA that provide instructions for creating proteins and RNA molecules. These components act as the cell's control system, determining its identity, function, and lifespan. During mitosis, DNA is replicated, and while the body has specialized repair mechanisms to fix errors, mistakes called mutations can still occur. While many mutations are silent because they happen in non-coding regions, others strike the coding DNA, altering the instructions for cell division.

A normal cell does not become cancerous overnight. It requires a cumulative 'domino effect' where at least about 6 or more mutations occur in the coding DNA. Some mutations might cause an overproduction of proteins that trigger division, while others might disable the proteins that signal a cell to stop. Once these errors build up, the cells divide so rapidly that they become less capable of repairing further damage, creating a cycle of accelerating mutation. These changes can be driven by natural processes, environmental carcinogens like tobacco smoke—which causes more than 4 out of 5 lung cancer cases—radiation, or inherited genetic factors such as the BRCA1 and BRCA2 genes.

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