What is Cancer Stage? An Oncologist Breaks it Down.

By: David Grew MD MPH

“How big is it and where else has it traveled?” 

∗ ∗ ∗

“What stage am I?” Usually this is one of the first questions I get asked when I meet a new patient with cancer.  It makes sense - most people are in search of a mooring or point of reference as waves of new information wash over them in the days following a new cancer diagnosis.  It’s even more charged, because for many patients cancer is the first time they stare face to face with their own mortality.  

In this blog, I’ve tried to compile the non-googleable (and non-chatGPT-able) insights and memory hooks I’ve picked up over the years.

Simply stated, cancer stage is a measure of how advanced a cancer is.  After 4 years of med school, 5 years of residency and 8 years of practice, here’s my staging for beginners:

  • Stage I - small cancer, hasn’t left the organ it started in, no lymph nodes
  • Stage II - medium size, hasn’t left the organ, maybe lymph nodes
  • Stage III - larger or involving lymph nodes
  • Stage IV - spread from original organ through the bloodstream, now in other organs

There are of course obvious exceptions.  Some node positive breast cancers are stage I.  Some node positive head and neck cancers are stage IV.  Brain tumors don’t use staging.  But generally these principles will keep you inside the lines.

When is staging done?  Right after a diagnosis, which involves a biopsy.  The biopsy answers the question “what is it?” Staging answers the questions “How big is it and where else has it traveled?” 

What tests are used for staging?  Different cancers have different required tests for staging, ranging from simple physical examination alone, to multiple scans like PET-CT or MRI. Usually some basic blood work is also involved.  The specific tests required depend on how that kind of cancer tends to spread.  So, since small cell lung cancer tends to spread to brain, we need an MRI.  But early stage breast cancer almost never spreads to brain, so we don’t get MRIs on everyone - unless they have concerning symptoms.

What is the purpose of staging?  It helps doctors select the best treatment.  Without staging, we would put patients through unnecessary surgeries when in fact chemotherapy was the best treatment.  Alternatively, well-staged patients may be able to de-escalate treatments, and safely omit treatments like chemotherapy or radiation without lowering the chance of cure.  In this sense we can avoid side effects and long term complications.  Staging helps us optimize for both cure and quality of life.

What is TNM staging?  TNM is an acronym for Tumor, Node, Metastasis.  We use this classification to objectively categorize each case of cancer.  Tumor is a measure of size (usually) and also whether the cancer is growing into adjacent organs.  If a cancer is small it is a T1 and as tumors are bigger we go up to T2-3 and eventually T4 which usually means it’s now growing into another adjacent organ.  Node refers to lymph nodes, which is the system that drains fluid from our organs as a way to filter out infections.  Since this is a common route of spread for cancer, we always try to objectively evaluate it in staging.  N0 means there’s no cancer in lymph nodes, and N1-3 means it is in the nodes, with the number depending on location of nodes  and how many are involved.  When lymph nodes are involved, it almost always changes treatment recommendations.  Metastasis is a word that means cancer has spread through the bloodstream and is now in a different organ system.  This definitely changes treatment, since surgery won’t solve this problem.  Typically we tackle this with treatments that are delivered into the blood, like chemotherapy, immunotherapy or other targeted therapies.

What is stage group?  The TNM information above is combined into a single number, called the stage group.  This is different and unique for each cancer.  Generally T1N0M0 is stage I, and anyT anyN M1 is stage IV, because metastasis is a game changer.  All the stage groupings in the middle are different combinations of TN scores and to be honest there are so many I usually refer back to the staging guidelines each time because it’s impossible for me to memorize all the combinations.  My brain doesn’t work like that and I see little value to memorizing them outside of flexing.

What treatments are USUALLY used for certain stages?  Early stage cancers are usually treated with “single modality” - which means just one treatment, typically surgery.  More advanced stages are usually tackled with “combined modality” treatments like surgery and chemotherapy with radiation.  The cleanest way I’ve come to understand this is “this cancer proved it is aggressive and has the ability to grow and spread.  We will ratchet up treatment intensity to match its aggression.” 

Does your stage change after treatment?  No.  Stage is always the initial stage.  If cancer is successfully removed, we would say “initially stage x, underwent y treatment, now with no evidence of disease in follow up.”  We don’t go to stage 0 once you’re done with treatment.  Talking about and understanding staging in this way tells the fuller story - how it started, what we did about it and how it’s going now.

Does stage change after a cancer comes back?  No.  Again, we always stick with the initial stage.  If it comes back we describe where it is now.  For example, “Initially stage III breast cancer, underwent partial mastectomy (lumpectomy), chemotherapy and radiation, now with recurrence in the breast.”  This way we can fully see the arc of treatment and most oncologists can easily intuit the next step in care.  In this case, mastectomy.

We made a short video for patients to better understand staging.  Not everyone is into blogs, so for visual learners a simple images to pair with the narrative might be useful.

Disclaimer - this is not medical advice.  There are obvious exceptions to some of the things written here.  Talk to your doctor before making any medical decisions.


How do doctors determine the specific tests required for staging different types of cancer, and what factors influence the decision to order additional scans like PET-CT or MRI?

Doctors determine the specific tests required based on various factors, including the type and location of the cancer, the extent of suspected spread, and individual patient characteristics. Factors influencing the decision to order additional scans like PET-CT or MRI include the aggressiveness of the cancer, the presence of symptoms suggesting metastasis, and the need for more detailed information to guide treatment planning.

Are there instances where staging might change treatment recommendations even if the initial diagnosis suggests a less advanced stage?

Yes, there are. This can occur if further testing reveals hidden metastases or if the cancer is found to be more aggressive upon closer examination. In such cases, treatment plans may need to be adjusted to address the newly discovered extent of the disease.

Are there any ongoing efforts or advancements in cancer staging techniques or classifications that aim to improve accuracy or streamline the staging process for clinicians?

Yes! This includes developing new imaging technologies, such as advanced MRI techniques and molecular imaging modalities, as well as refining existing staging systems to better reflect the biology and behavior of different cancer types. Additionally, there is ongoing research into the use of biomarkers and genetic profiling to provide more personalized and precise staging information for individual patients.