Last reviewed 1 June 2026
Cancer is not one disease but a family of related diseases. It begins when some of the body’s cells start to grow and divide without the usual controls, and can spread into surrounding tissue. Because it can start in almost any part of the body, there are many types — and they behave, and are treated, very differently.
Our cells normally grow, divide and die in an orderly way. Cancer develops when changes in a cell’s genetic instructions let it keep dividing when it should stop. Most of these changes happen by chance over a lifetime; some are linked to things we are exposed to, and a smaller share are inherited. This is why cancer becomes more common as we age — and why no single cause explains it.
A few terms come up again and again. A tumour is a lump of cells — benign means it does not spread, malignant means it can. Stage describes how far a cancer has grown or spread; grade describes how abnormal the cells look. Metastasis means cancer cells have travelled to another part of the body. Understanding these words makes every conversation that follows easier — and our glossary explains many more.
You do not need a medical degree to understand cancer. Knowing the basics helps you recognise symptoms sooner, follow a diagnosis conversation, and ask better questions — for yourself or for someone close.
This guide is based on public guidance from European cancer institutes and public health authorities, written in plain language.
Common misconceptions about cancer, calmly and clearly corrected.
Food, movement, alcohol, sun and tobacco: what the evidence actually says.
Which programmes exist, who they are for, and why timing can matter.
How to tell trustworthy sources from myths and sensational claims.
Words that help, questions to ask your doctor, and supporting someone close.
