Hi everyone, I'm Prateek and in this video we're going to be looking at the TNM classification,
which is a method of classifying cancers. If you want to see more educational videos, similar to
this, then please make sure to subscribe to this channel. The TNM classification is a method of
staging a cancer - so it's looking at how big the primary cancer is, where it has spread to
locally in terms of lymph nodes and also if it has spread to any other parts of the body.
Staging cancer is very different from grading a cancer. Grading is where we look at how similar
the cells of the cancer are to normal healthy cells and this is handled in a different way.
So the TNM system has three parts to it - we have T which is the tumour and this looks at the size
of the tumour as well as the depth of invasion of the tumour. We have N which is the lymph nodes
and this looks at whether the cancer has spread to lymph nodes, how many lymph nodes, the size of the
lymph nodes and whether the cancer has broken out through the lymph node or extranodal extension
and then we have M which is metastasis and this is looking at whether the cancer has spread to
other parts of the body. This form of staging is used for all cancers of the body, however in this
video for simplicity we're going to be focusing on cancers of the oral cavity. Additionally, we'll be
looking at the TNM-8 system which was put in place in 2018. Currently in most staging, both the TNM-7
and the TNM-8 systems are used, however I will discuss what the key differences are between
the TNM-7 system and the TNM-8 system towards the end of this video. So let's first look at T - the
tumour. We have Tx - this is where the tumour cannot be evaluated. We then have Tis which is a carcinoma in
situ and this is simply a very early cancer that hasn't spread through more than one layer of the
tissue. Then we have T1 - this is where the tumour at its greatest dimension is no greater than two
centimetres. Additionally, the depth at which the tumour has invaded at, the depth of invasion, is no
greater than five millimetres. So we have a maximum tumour dimension of two centimetres or less and the
maximum depth of invasion of five millimetres or less. We then have T2 and this is where either the
tumour is two centimetres or less in its greatest dimension but between five and ten millimetres in
terms of depth of invasion or a tumour is size in its greatest dimension between two centimetres and
four centimetres but the depth of invasion is no greater than 10 millimetres. We then have T3
and this is where the tumour is either greater than 4 centimetres in its greatest dimension or
any tumour that has a depth of invasion greater than 10 millimetres. And then we have T4 - T4 is
essentially moderately or very advanced cancer. So in the oral cavity, we have T4a and this indicates
a tumour that has invaded into surrounding tissues. So, for example the oral cavity, it may have spread
into the mandible, it may have spread into the sinuses. We also have T4b where the tumour has
spread even further and has gone into the muscles of the face or alternatively has gone to the skull
base. Additionally, it could be surrounding vital arteries - this essentially indicates
a very advanced cancer. Now let's look at the lymph node involvement and for this lymph nodes
can be assessed clinically or pathologically. So clinically would be when a patient first presents
to you and you assess them and it is kind of the feel that you get when you're assessing their
lymph nodes. Pathological staging is done once the surgery is carried out and we actually physically
look at the lymph nodes to see how significant the cancer was. So for the purposes of this video
I'll be looking at the pathological lymph node staging for oral cavity cancers.
Again we have an Nx - this is where the lymph nodes could not be evaluated. We then have N0
which is that there is no lymph node involvement whatsoever. We then have N1 - this
is where the cancer has spread to a single lymph node on the same side, or the ipsilateral side,
of the primary tumour. Additionally, the node is no greater than three centimetres in size and there
is no extranodal extension. So extranodal extension, previously referred to as extracapsular spread,
is where the cancer essentially burst out of the lymph node and is impacting surrounding tissues.
Next, we have N2a again there are two potential scenarios for this. So the first one is that we
have a single lymph node, on the same side of the primary tumour that is still three centimetres or
smaller but there is extranodal extension. Alternatively, it could be a single lymph node
on the same side of the tumour between three and six centimetres but it hasn't got any extranodal
extension. Next we have N2b, this is where there is more than one lymph node that has been affected
by the cancer on the same side of the tumour but none of these lymph nodes are greater than six
centimetres in size. Additionally, there is no extranodal extension. We have N2c where the cancer has
spread to more than one lymph node on either side of the body, so the ipsilateral and contralateral
side but none of the lymph nodes are greater than 6 centimetres in size again there is no extranodal
extension. Next stage up we have N3a. N3a is where there is any single lymph node that is greater
than six centimetres in size and there isn't any extranodal extension. And finally we have N3b - N3b
essentially focuses on extranodal extension. So in N3b, we either have a single lymph node on the
same side as the tumor that is greater than three centimetres in size and has extranodal extension or
the cancer could have spread to many lymph nodes and of these one of them has extranodal extension
or there is extranodal extension of a single lymph node on the opposite side of the tumour, so the
contralateral side, but this is three centimetres or less in size. So that looks at the node stages
and finally we have M which is metastasis and this is relatively straightforward. So we have
M0 where the cancer has not spread to other parts of the body or M1 where the cancer has spread to
other parts of the body. And this makes up the TNM classification. So if we had an example of a T2
N1 M0 cancer. This would be a tumour that is two centimetres or smaller in its maximum dimension
but has a depth of inversion between five millimetres and ten millimetres or
a tumour that is between two centimetres and four centimetres in its maximum dimension
but a depth of invasion less than ten millimetres. We have the N1
this would be a single ipsilateral lymph node that is no greater than three centimetres in size
and has no extranodal extension and we have M0. So the M0 means that there is no distance metastasis.
Now I mentioned at the start of the video that this is the TNM-8 system. So between the TNM-8 and
the TNM-7 system there are two key differences for cancers of the oral cavity. The first one
is that we look at the depth of invasion in the T stage, so looking how far that cancer has gone into
the tissues and the second big one is that we now look at extranodal extension in the node stage, so
looking at whether the cancer has spread out of the local lymph nodes. The reason these two things are
included in the classification system now is that we know that they are important prognostic factors
with regards to a patient's cancer and will have quite a big impact on the likelihood of success
of any treatment. My recommendation in this video is the Clinical Problem Solving in Dentistry book.
This book is excellent for any viva preparation particularly those who are coming towards finals. I
know when I was in dental school I struggled with vivas a fair amount, however this book takes you
through step-by-step on how to answer questions and it's a book that I always recommend to final
year students. If you found this video useful, please make sure to like, comment and subscribe
and if you have any suggestions of any other videos that you'd like to see, please leave a
comment below or contact me on one of the social media handles. Until the next video, take care!