Melanoma TNM Staging – Breaking Down What All Those Letters and Numbers Mean

In my previous post, I talked about the new changes to the guidelines for diagnosing and treating melanoma. One of the changes affects the definitions of melanoma stages. But I realized as I was talking about those changes that some people may not know what all of those letters and numbers mean.

To complicate matters further, there are actually a couple of different methods of staging. I’ll talk about those other methods in a later post, but this post is going to focus on what is referred to as TNM staging.

TNM means it defines the Tumor or lesion, Nodes that may be involved, and Metastasis (TNM). Let’s start with T – Tumor. There are actually two components to this element: the thickness of the tumor and ulceration. Thickness refers to how deeply the melanoma has grown into the skin. Ulceration means whether the skin is broken over over the tumor. So when the dermatologist asks you if that suspicious spot bleeds, she’s looking to answer that ulceration question. It used to be that ulceration was denoted by an “a” or “b” after the numbers. The updates have changed that slightly.

So, thickness… keep in mind that thickness here means: how deeply has the melanoma lesion penetrated the skin.

Quick anatomy lesson: your skin is made up of the epidermis, the dermis, and a fat layer (aka fascia).

The epidermis is the outermost layer of your skin and is between 0.5 and 1.5 mm thick. It is not just dead skin cells. The epidermis has immune cells working within it. But there are no nerves or blood vessels in this layer. This is the barrier that protects you from basically everything in the outside world.

The dermis is the next layer and it’s generally 1.5 – 3.0 mm below the surface. This layer has connective tissues and immune cells as well as a network of blood vessels and nerves. When you burn yourself, the burn has to hit the dermis for your body to register the pain. Same thing if you cut yourself. This layer is really about making your skin firm but elastic. It is also the place where the inflammatory processes occur, sending immune cells to combat microbes that somehow have made their way past the epidermis.

Below the dermis is a layer of fat that contains blood vessels but is mostly collagen. This layer is important in making sure that everything can move flexibly (among a whole bunch of other important things).

Ok, back to that T… As mentioned, the updated guidelines address how lesions should be categorized. I’m going to use the new guidelines to define the terms below:

• Tis (I’ve sometimes seen this referred to as T0) – this means the melanoma cells are only found “in situ” or within the very top layer of skin. Basically, it’s surface-level melanoma in your epidermis.
• T1a – a lesion is less than 0.8 mm deep and is not ulcerated
• T1b – under the new guidelines, this can mean one of two things: any lesion, ulcerated or not, with a thickness between 0.8 and 1.0 mm OR any ulcerated lesion less than 0.8 mm thick
• T2a – the lesion is greater than 1.0 mm up to 2.0 mm in depth and is not ulcerated; this melanoma is getting into your dermis level
• T2b – same thickness as above but the tumor is ulcerated
• T3a – the tumor thickness is greater than 2.0 mm up to 4.0 mm and is not ulcerated
• T3b – an ulcerated lesion that is between 2.0 mm and 4.0 mm
• T4a – any lesion with a thickness greater than 4.0 mm but does not have ulceration; this lesion has likely penetrated through both the epidermis and dermis layers and is hitting the fascia
• T4b – an ulcerated tumor with a thickness greater than 4.0 mm

Summing up so far, we’ve looked at how deeply the melanoma has penetrated the skin and whether the lesion is ulcerated. Ulceration has been shown to be an indicator of how your melanoma is progressing; recent research indicates it may predict how your melanoma responds to using an immunotherapy called adjuvant interferon.

OK, moving along to the N. This denotes whether there are melanoma cells in nearby lymph nodes.

• N0 – no nearby lymph nodes contain melanoma cells
• N1 – melanoma cells are in one lymph node
• N2 – melanoma cells are found in 2 or 3 lymph nodes
• N3 – 4 or more lymph nodes contain melanoma cells

The N section also contains letters – because what’s a little more complexity to a patient struggling to understand exactly what the diagnosis means, right? In order to severity:

• Na – the melanoma in the lymph nodes can only be seen by a microscope or what is referred to as micrometastasis
• Nb – obvious signs of melanoma in the lymph node – aka macrometastasis
• Nc – the melanoma cells are also in areas of the skin very close to the primary location (what’s called satellite metastases) OR in the lymph channels in the skin (in transit metastases)

Obviously, Nc is not good because it shows that the melanoma cells are migrating away from the primary location of the lesion.

And M simply refers to whether the cancer has spread (i.e. metastasizing).

• M0 – the cancer hasn’t spread anywhere else
• M1 – the cancer has metastasized

Not to be left out, M1 gets letters too and these are not letters anyone wants to get in their inbox…

• M1a – melanoma cells are in the skin somewhere else in the body OR melanoma cells are in lymph nodes far away from the initial lesion
• M1b – melanoma cells are present in the lung
• M1c – melanoma cells are in other organs OR the melanoma is causing your liver to create a high level of lactate dehyrogenase (high levels indicate tissue damage and/or whether a cancer treatment is working or not)

There you have it, TNM staging broken down. While your dermatologist should spend the time to review your pathology reports with you until you completely understand the implications, it is also a time when you are basically the “deer in the headlights”. Throwing a combination of letters/numbers/more letters at you when your brain is screaming, “What the hell is she talking about?? Am I going to die?” means that the message doesn’t always translate. Or even worse, family members start asking you “what does all this mean” and you’re really not in the mood to play doctor. So if your pathology report is TNM-based, you can just point them to this page…