What is Cancer?
Understanding the Basics
Cancer is a word that carries a lot of weight.
For many people, it brings fear, uncertainty, and a feeling of losing control. And often, it is not just the disease itself that feels overwhelming – it is also the language around it.
So let’s start at the very beginning.
What is cancer, really?
At its core, cancer is not one single disease.
It is a group of conditions where certain cells in the body begin to grow in a way they shouldn’t.
Our bodies are made up of billions of cells. Normally, these cells grow, divide, and die in a very controlled and organised way. This process keeps everything in balance.
Cancer begins when that balance is disrupted.
Some cells stop following the rules.
They grow when they shouldn’t.
They don’t die when they should.
And over time, they can form a mass or spread to other parts of the body.
A simple way to picture it
Imagine your body as a garden.
In a healthy garden, everything grows in harmony. Plants have their place, weeds are kept under control, and there is a natural balance.
Now imagine that some plants start growing out of control.
They take up more space than they should.
They don’t respond to pruning.
And they begin to affect the surrounding plants.
The result of that uncontrolled growth is what we call cancer.
How does cancer begin?
Cancer usually develops over time.
Inside our cells, there is a kind of instruction manual – our DNA. It tells cells when to grow, when to repair themselves, and when to stop.
Sometimes, changes occur in this instruction manual. These changes are called mutations.
Most of the time, the body can fix these mistakes.
But sometimes, it cannot.
When enough of these changes build up, a cell may begin to behave differently – and that is when cancer can start to develop.
Is cancer always a tumour?
Not always.
Some cancers form a solid mass, often called a tumour. But not all cancers do.
Blood cancers, for example, affect the blood or the lymphatic system and do not form a lump. They still behave like cancer, but they grow in a different way.
And it also works the other way around:
Not every tumour is cancer.
A tumour simply means that there is a growth or a lump. This can be harmless, like a wart or a cyst. These are called benign tumours and they do not spread like cancer.
So:
- Not every cancer forms a tumour
- Not every tumour is cancer
Understanding this difference can already take away some of the fear around the word “tumour.”
We will explore this in more depth in a later chapter of this blog.
Can cancer spread?
Yes, some cancers can spread from where they started to other parts of the body.
This process is called metastasis.
Going back to the garden:
It’s like seeds being carried by the wind and starting to grow in other areas of the garden.
Not all cancers spread, but understanding this process helps explain why early detection can be important.
What are the hallmarks of cancer?
You may now be wondering what actually makes cancer behave the way it does. Why do some cells grow uncontrollably? Why do they spread, and why can they sometimes resist treatment?
To answer these questions, scientists have identified what are called the hallmarks of cancer. These are common patterns or abilities that cancer cells develop over time – almost like a set of skills that allow them to survive, grow, and spread within the body.
Understanding these hallmarks can help you see the bigger picture. It’s not just about a single tumour or diagnosis, but about how cells change their behaviour in ways that make cancer what it is.
In the next post, we’ll gently walk through these hallmarks together and break them down into clear, understandable pieces – so you can feel more confident navigating this part of the cancer journey.
Want to dig deeper?
If you’d like to understand terms like tumour, benign, or metastasis more clearly, you’ll soon find more dedicated articles here on the blog — each one breaking down a single concept in a simple, visual way.
If you want the whole structured journey, where everything connects step by step, you can also explore my book How to Speak Cancer.
It brings these topics together step by step and supports you in navigating the language of cancer at your own pace. Along the way, you will also find additional support, including links to patient organisations, glossaries of cancer and clinical trial terms, and a notes section where you can write down your own thoughts, questions, and key points to help you prepare for your next appointment with your healthcare team.