Ok, as I was typing that title, I was thinking to myself, didn’t I got to high school with Clark Breslow? But actually, his first name is Nate. Hopefully he never needs to read a blog about melanoma, but if he does – what’s up dude? Still got your skateboard?
Anyway, for those of you that actually come to this blog to read about skin cancer stuff, in today’s post I’m going to review the two other melanoma staging models. If you can’t guess by the title of this post, one is called Clark and the other Breslow (and if you couldn’t guess, my brand of sarcasm is likely lost on you as well).
OK, let’s start with the news that the American Joint Committee on Cancer (AJCC) staging system no longer uses these staging classifications because the TNM model described in the last post has replaced them. BUT, some dermatologists or pathologists still refer to these numbers in their biopsy reports (mine did in 2014 even though the 2011 AJCC guidelines supposedly did away with Clark and Breslow). So this post may one day be as antiquated as instructions on how to use a rotary-dial telephone.
Both the Clark and Breslow scales measure how deeply the melanoma has penetrated the skin. So going back to the TNM staging, both of these scales measure a portion of the T element (reminder, T is for tumor and both thickness and ulceration are denoted by the combination of numbers and letters following the T).
The Clark scale looks at two things: one, how deeply the melanoma has grown into the skin; and two, which levels of the skin have been effected. Remember the quick anatomy lesson from the last post? Skin is the epidermis, dermis, and the fat layer (called the subcutaneous layer or hypodermis in the stock photo below – sorry for the weird colors, but do you know how hard it is to find a photo that gets as detailed on the skin layers as this one to help illustrate the Clark levels?).
There are five levels in the Clark scale:
- Level 1 – melanoma in situ; meaning the melanoma cells are found only in the outer layer of skin, the epidermis
- Level 2 – melanoma cells are in the papillary dermis, which is the layer directly under the epidermis
- Level 3 – melanoma cells are through the entire papillary dermis and touching the reticular dermis, which is the next layer down
- Level 4 – melanoma cells are through into the reticular dermis
- Level 5 – melanoma cells have grown into the fat layer
I think you can see why the AJCC did away with the Clark scale. If you’re not extremely well versed on your fine-grained anatomy of the skin layers, the levels are pretty much meaningless – except for 5 because let’s face it, if cancer is staged from 1 being the least worst and 5 being the worst, you know if you have the highest number, things are not good.
So that leads us to the Breslow model. This one is pretty easy to understand in comparison to Clark. The pathologist measures the thickness or how deep the lesion has grown into the skin using a micrometer. You know how in the TNM model your T number depends on how many millimeters deep the lesion has grown? That’s pretty much your Breslow number. Your tumor is 3 mm deep? Your Breslow number is 3.
So while I might complain a bit about the complexity of the TNM model, it actually provides a hell of a lot of information within all of those letters and numbers.