Okay. That's “Grading” - How does
the tumor look down the microscope?
“Staging” on the other hand general principles,
this takes into account, everything
that is known about the patient,
not just under the microscope so
whether there's metastatic disease.
What other parts of the tumor have
affected in terms of the original site
of origin, that kind of stuff.
So, the tumor staging is through a “TNM” system.
The “T” stands for tumor size and
location and depth of invasion
and in these TNM systems, it's
also unique for every tumor type.
So, lung cancer has a different TNM
system, than does prostate cancer,
than does breast cancer, than does brain cancer,
so, we've developed a different
TNM system for them all
and again, don't expect you to memorize those,
but to be aware of those, because
they impact prognosis and therapy.
So, “T” in the TNM system stands for
tumor size location depth of invasion.
“N” stands for lymph node involvement,
whether it's positive or not and the
total lymph nodes that are involved.
So, the T grade can be for example, T1
to T4 depending on the size and location
and depth of invasion.
The nodal involvement can be N0, no nodes,
N1, one node, N2 more than one node.
So, again the staging here depends on
the particular TNM system
in the particular tissue.
And “M” is whether there are distant
metastasis present or absence.
For every distinct tumor type, that TNM value,
is translated to a stage 1-4.
And as I said before, every
single one of these TNMs,
varies from tumor type and tissue.
So, the long TNM system is
different than the prostate,
is different than the breast etc.
The important thing about this staging system,
which also, sometimes
incorporates the grade as well,
it allows patients to be categorized
into high risk, medium risk,
low risk for bad outcome.
And that will tell us whether to be
very aggressive with their therapy
or whether we can be a little bit
more laissez faire about that.
Okay. So, when you become oncologist,
you will learn this system
for your specialty tumor.
Right now, just be aware that that's
how grading and staging works.
Let's think for a minute now about staging,
just a good example is colorectal cancer staging
and on this image, we're looking
down the barrel of this colon,
we have the lumen, we have the mucosa
where cancers are going to originate,
we have the submucosa, we
have the muscularis propria,
and we have the serosal outer lining.
If a tumor is reasonably small
and is it's constrained to either,
the epithelium or minimally
invasive into the submucosa,
then it's a stage one tumor.
If it is more deeply invasive
into the muscularis propria,
then it's a stage two tumor.
If it goes all the way
through the muscularis mucosa
and into the serosal surface,
this is a stage three tumor,
and a stage four tumor,
will have lymph node metastasis.
So, that's kind of gives you a general
sense of how we would do staging,
say in colon cancer.
Why do we care about all this?
I’ve already kind of mentioned it.
What stage you are at the time of your diagnosis,
will tell you and your oncologist
your survival likelihood
and how aggressive you should be in therapy.
So, stage 0, is actually carcinoma
in situ, in colon cancer staging,
it doesn't invade beyond the basement membrane
and stage 1, stage 2, stage 3, and stage 4,
are what you see in the different colors
and you can see that if you're
stage 4 disease with colon cancer,
you have a very poor prognosis.
In fact, about half of the patients
with that will be dead within 10 months,
So, that says in that population
based on the staging characteristics,
I’m going to be really hyper-aggressive,
if I’m going to try to
treat and help that patient.
Stage 3 disease in comparison, has about
a 50% mortality at more like three years,
okay and then stage 2, stage 1, stage 0, etc.
So, this allows us to stratify
risk, stratify prognosis
and stratify potentially therapy and with that,
we've kind of covered grading and staging.