How Does the Cancer Staging System Work?

You may have heard someone refer to “stage one breast cancer” or “stage three lung cancer” and wondered what it meant. The staging of different cancers can give you information about the extent or severity, helping your medical team or loved ones to understand what you are dealing with.

What is cancer staging?

When you are diagnosed with cancer, any information gained about your cancer can be used to categorise it according to a staging system. Details such as location, spread, and size are important. Once a stage has been assigned, it can be used to easily loop others into what you are dealing with, to assess treatment plans, and to establish possible outcomes. The stage usually refers to the state of cancer at diagnosis, even if cancer changes over time.

Why is cancer staging important?

Information that is helpful to understanding, treating and describing your cancer includes the stage, grade and type. Today we will focus on the stage. Staging helps your medical team decide on the initial best course of action, or which treatments are needed. The treatment that would be the best fit will depend on the size, location, spread, and more. 

The assigned stage can assist in predicting the course that cancer will take, as well as predictions for survival and treatment success. Staging systems create common categories that include essential information about the anatomy and extent of disease, and can therefore be used with ease between medical professionals when communicating about cancer, or when conveying the seriousness of the disease. 

Staging also makes it easier to compare treatment results in research, brings consistency into cancer management reporting, and can be used in treatment guidelines to create simplified standards. 

What information is needed for cancer staging? 

Staging happens once you get a cancer diagnosis before any treatment decisions are made. When someone is diagnosed, different information is taken into account in order to categorise it by stage. Some sources of information that your doctor may take into account are physical exams, imaging, endoscopies, biopsies, and lab tests. There are many other factors that can affect staging, including the grade (a measure of how developed/organised the cancerous cells appear), cell types, biomarkers, and age. Which information is relevant to the categorisation of cancer depends on the type of cancer and staging system used, as they differ.  

Cancer staging systems explained 

It is important to note that there are several staging systems, and the factors that are taken into consideration when staging is varied depending on the type and location of cancer. Below is a brief overview of two commonly used systems. 

TNM staging

This is one of the most used staging systems. TNM refers to ‘Tumour’, ‘Node’, or ‘Metastasis’, each of which is evaluated in order to allocate a number (or in some cases, letters).

1. Tumour (T)

The original or primary tumour is what your doctor will describe, as this is where cancer started. The size, location, and growth would be assessed, as to whether there are other tumours nearby. Possible descriptions include:

• X (e.g. Tx): Indicates that there is no information about the primary tumour, or that the tumour cannot be measured
• 0 (e.g. T0): Indicates that no evidence of the primary tumour, or that the tumour cannot be found.
• Tis: Indicates ‘in situ’ (in place) cancer, meaning that the cancer cells have not grown beyond the layer of cells in which they started.
• 1-4 (e.g. T3): The numbers between 1-4 may refer to the size or depth of the primary tumour, or to the nearby spread. The size correlates with the numbers (smaller number = smaller size/less growth).

2. Nodes (N)

The second area to assess is the lymph nodes. Lymph nodes are small immune cell collections, and many cancer types spread to the nearest lymph nodes first before going on to other parts of the body. Your doctor will assess the nodes near the primary tumour, as their presence is a sign that cancer has begun to spread (sometimes referred to as positive lymph nodes). 

• X (e.g. Nx): Indicates that there is no information available about lymph nodes near the primary tumour, or that the notes cannot be evaluated 
• 0 (e.g. N0): Indicates that the nearby nodes do not contain cancer
• 1-3 (e.g. N2): Indicates the size, location, or number of affected nodes nearby. Higher numbers indicate a greater spread

3. Metastasis (M)

Finally, the spread of cancer across the body is assessed. Doctors may need to asses other body parts in order to find out how far the cancer has spread from the primary tumour. 

• (e.g. M0): Indicates that no cancer has been found far from the primary tumour (absence of metastases)
• 1 (e.g. M1): Indicates that cancer has spread to distant organs or tissues (presence of metastases) 

Number staging

Number staging is the system that most of us have been exposed to. This method of categorization combines the TNM staging system with other relevant information, grouping cancer into 4 general stages numbered 1-4 (often written in Roman Numerals as demonstrated here, and sometimes subdivided further using capital letters). Generally speaking, lower numbers indicate less advanced cancer and a better prognosis.

• Stage 1 (I): Generally indicates that the cancer is small and contained within the organ where it started (no spread).
• Stage 2 (II): Generally indicates a larger tumour (compared to stage 1), but cancer has not spread into the surrounding tissue. However, depending on the type of cancer, Stage 2 could also refer to cancerous cells that have spread to the nearby lymph nodes. 
• Stage 3 (III): Generally indicates a larger cancer, possibly one which has spread into nearby lymph nodes as well as surrounding tissues.
• Stage 4 (IV):  Also called secondary, advanced, or metastatic cancer. Generally indicates that cancer has spread from where it began to at least one other organ.
• Stage 0: Some cancers have the option of a stage 0. This stage indicates that abnormal cells are present, but have not spread from the layer of cells where they started. 

Another staging system (used more by doctors than registries) can be used to group all types of cancers into main categories:

• In situ: Abnormal cells present, however, they haven’t spread to nearby tissue.
• Localised: No sign of spread, cancer remains where it started.
• Regional: Cancer has spread to nearby lymph nodes, tissues, or organs.
• Distant: Cancer has spread to an outlying body part.
• Unknown: Not enough information to allocate a stage.

Every cancer type has its own TNM categories, therefore the above is only common example as letters and numbers don’t mean the same for all the types. In addition, some cancer types have subcategories for the TNM staging system, while others don’t have as many categories as the original system. 

Other cancers do not assess the same factors as discussed here and therefore are staged differently. For example, Leukemia is in the blood and spread usually occurs before the cancer is found, and brain cancer doesn’t generally spread to other parts of the body or the lymph nodes, therefore the mentioned systems may not be appropriate. 

Staging can also be organised into different types, for example:

• Clinical staging (how much cancer is based on examination and tests)
• Pathological staging (determined during surgical tumour removal, usually combined with clinical staging results)
• Post-therapy / post-neoadjuvant therapy staging (how much cancer remains after systemic therapy or radiation therapy)
• Recurrence/retreatment staging (extent of disease if cancer recurs post-treatment)

Due to the varied nature of staging systems and the new discoveries about cancer that our medical professionals constantly need to incorporate over the years, it is recommended that you speak to your doctor for clarity and understanding about a cancer diagnosis and its stage. Our team at GlobMed is right at your fingertips, book a consultation now to get the support you need.