Dr. Eric Vallières, thoracic surgeon, reviews the structure and purpose of staging using the current tumor-node-metastasis (TNM) system for lung cancer.

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So, the first concept that I would like to cover today is the TNM concept, which is what we use to stage lung cancer, and other cancers, but in lung cancer in particular. We use the T, which stands for tumor, and it’s usually in relation to either the size or the location of the lesion; the N sounds for nodal disease, or nodal involvement, or absence thereof, and the M stands for metastasis, or a tumor that has spread away from its original bed, beyond the lymph nodes and the lymphatics.

In lung cancer, we subdivide at this stage, and that may change in the years to come, but right now we’re subdividing the T stage, the T descriptor, into 1, 2, 3, and 4, depending on the size of the lesion, depending on the location of the lesion, and whether or not there are other structures involved by the tumor itself, beyond the lungs. For example, if a tumor of the lung is directly invaded into the ribs, which is the chest wall, that is a T3 by definition of the descriptor T3.

The T1 lesions are the small little lesions that are not invading any structures, and as the tumors grow — so there’s a T, so T2 lesions are lesions that are larger, and T3 as well. The T4 lesions are lesions that are invading into structures that are considered, or historically were considered, to be non-operable, non-surgical, though that has changed over the years, but for a very limited number of patients.

The N descriptor relates, as I said earlier, to whether or not there is tumor into the lymphatics or the lymph nodes in the lung or around the lung, and the N descriptor will either be a 0, a 1, a 2, or a 3. 0 means the lymph nodes were examined, and there was no evidence of cancer in them. If no lymph nodes were examined, if for some reason during surgery there were no lymph nodes removed, the pathologist will put a descriptor X, meaning that we don’t have that information on hand.

If the lymph nodes within the lung itself are involved, any number, it’s an N1. Once lymph nodes that are outside the lung are involved, it’s at least an N2, and if those nodes are further away from the lung itself, either on the other side of the midline, or higher up at the root of the neck, it becomes an N3. That’s the highest number that we can put to the nodal descriptor.

The M descriptor relates to a metastasis or not, so M0 means there are none, and M1 means there are. Now we have an M1a, M1b, depending on which areas are affected by metastasis, but in general, the treatment is all the same.

Now, those descriptors, we group them together depending on whether it’s a T1, N0, M0, or a T1, N2, M0, and we group them together and we define a stage. The stage is really what determines how we treat patients, as per established lines of care and standards of care.