In Situ, Localised, Metastatic
How Cancer Spreads
When cancer is discussed, one of the first things doctors try to understand is how far it has spread.
You might hear terms like in situ, localised, or metastatic.
They can sound technical — and sometimes alarming — but they are simply ways of describing where the cancer is and how it behaves.
Understanding these words can help you follow conversations more easily and feel a little more oriented in a situation that may feel uncertain.
Let’s take this step by step.
A simple way to picture it
Let’s return to the garden.
Imagine something new beginning to grow.
At first, it’s just a small change — barely visible. Over time, it may grow, stay contained, or spread to other parts of the garden.
These stages help describe that process.
What does in situ mean?
In situ means “in its original place.”
At this stage, the abnormal cells are present — but they have not moved beyond where they first started. They have not invaded surrounding tissue.
It’s like a seed that has settled into the soil but hasn’t yet spread its roots beyond that exact spot.
Everything is still contained.
Because of this, cancers detected at this stage are often easier to treat, as they have not yet spread.
What does localised mean?
Localised means the cancer has grown, but it is still limited to one area of the body.
It may form a tumour and begin to affect nearby tissue, but it has not spread to distant parts.
Now the seed has grown into a small plant.
It’s visible and established — but still growing in one “pot” or one section of the garden. It hasn’t spread to other areas.
At this stage, treatment often focuses on removing or targeting the cancer before it spreads further.
What does metastatic mean?
Metastatic cancer means the cancer has spread from where it started to other parts of the body.
This happens when cancer cells travel — often through the blood or lymphatic system — and begin to grow in new locations.
This process is called metastasis.
This is when seeds from one plant are carried to different parts of the garden.
New plants begin to grow in other places, away from the original one.
Because the cancer is now in more than one location, treatment often becomes more complex and may involve different approaches to manage it across the body.
Why this matters
These terms help doctors understand:
- how advanced a cancer is
- where it is located
- how best to treat it
They are not labels — they are tools that guide decisions.
And while the words can sound heavy, they are describing what is happening in the body to give you the best care possible.
A gentle reminder
Hearing that cancer has “spread” can feel overwhelming.
But these terms do not define everything:
- not how a person will respond to treatment
- not what their individual path will look like
- not what is possible moving forward
They are part of understanding the situation — not the whole story.
Understanding how cancer spreads can help you make sense of what you’re being told, ask clearer questions, and feel a little more grounded in the process.
Just like in a garden, growth can take different paths.
What matters is understanding what’s happening — and having the right support to respond to it.
Want to dig deeper?
If you’d like to understand terms like tumour, mass or benign and malignat more clearly, you’ll 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.