When the body's internal instructions for cell growth break down

Science · Published 25 October 2026 Swipe more like this →

In short: Your body is a masterpiece of regulation, where cells grow, die, and replace one another in a perfect cycle. Cancer occurs when this orderly process fails. Instead of following the rules, some cells begin to multiply uncontrollably, transforming from healthy tissue into malignant tumors.

Cancer is fundamentally a disease of uncontrolled cell division. In a healthy body, cells multiply to create new tissue and die off when they are old or damaged. However, genetic mutations can disrupt this regulation, causing abnormal cells to grow when they shouldn't. These cells can cluster into lumps of tissue known as tumors. These mutations involve specific genetic elements like oncogenes and tumor suppressor genes. The disease can originate in almost any part of the human body, which contains trillions of cells.

There is a critical distinction between benign and malignant tumors. Benign tumors do not invade nearby tissues or spread to other parts of the body, and they usually do not grow back once removed. In contrast, malignant tumors are cancerous; they invade surrounding areas and can travel to distant locations to form new tumors, a process known as metastasis. While malignant tumors are the primary concern, some benign tumors can still be life-threatening. For example, a benign tumor located in the brain can cause serious symptoms despite not spreading.

Cancer cells possess several unique survival mechanisms that distinguish them from normal cells. They can grow without receiving growth signals, ignore instructions to undergo programmed cell death (apoptosis), and even trick the immune system into protecting them rather than attacking them. Some cells even signal for blood vessels to grow toward the tumor to supply oxygen and nutrients. To fuel their rapid expansion, some cancer cells utilize different types of nutrients than healthy cells. They may also generate energy from these nutrients in ways that differ from normal biological processes.

The biological complexity of cancer is vast, with more than 200 different types identified. Some, like leukemias, are cancers of the blood and do not form solid tumors. At a genetic level, cancer cells often accumulate multiple changes in their chromosomes, sometimes even doubling the normal number of chromosomes to fuel rapid growth. In the United Kingdom, approximately 1 in 2 people will be diagnosed with cancer during their lifetime. This highlights the prevalence of the more than 200 distinct types of the disease.

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