A skin biopsy is a procedure where your doctor samples skin so it can be examined under a microscope. It is usually done to diagnose skin cancer or an unusual rash.
How Is Skin Removed?
A small slice is taken as a shave biopsy with a scalpel
. If a deeper sample is needed, the biopsy may be done in a core fashion with a small ‘punch’
. If a large portion of skin needs to be tested, an excision
may be done. No matter how the sample of skin is taken, there will be some bleeding. A little wound is created that has to heal and a scar may form. Don't worry! You'll receive a shot to numb the skin first.
A skin biopsy allows a trained physician to examine your skin's layers and cells.
The skin is ‘rubberized and dyed’ and thinly sliced, then mounted on a glass slide. For technical and chemistry reasons, this process takes at least a few days for a diagnosis. Even then, a specific diagnosis is often not obvious. I explain this ambiguity to patients with the Asian pear analogy:
Some Asian pears look obviously like Asian pears. Others look like apples, some like pears. Some look like neither a pear nor an apple.
Similarly, sometimes the doctor at the microscope can’t tell if your sample looks or doesn't look like a specific diagnosis. It may be the doctor is not familiar with skin's subtleties - just like some people don’t know how Asian pears differ from pears and apples.
That’s the crux of a study just released in the British Medical Journal
Who Looks At Your Biopsy Is Important
In the BMJ article,
240 skin biopsies of suspicious moles were sent to 187 pathologists twice, at least 8 months apart. The pathologists were at a consensus when the moles appeared either normal or obviously cancerous. In the more intermediate cases (aka Asian pears), the pathologists were not so consistent. In fact, it was estimated about 20% of the worrisome moles would get a different diagnosis when examined by an expert pathologist.
Experience matters in pathology.
Who Determines Your Diagnosis?
Dermatologists learn how to microscopically examine skin in our residency training. Pathologists also learn this. There are also dermatopathologists
who get additional training after doing a dermatology or pathology residency. They examine so many skin biopsies in the course of this extra training and for the rest of their careers that it’s mind numbing. These are the experts.
Who looks at your biopsy is important and you should ask who will be looking at your skin sample under the microscope.
I use dermatopathologists in teaching medical centers for my patients' biopsies because they are the super experts that define what is right, wrong, and new in the field. Even then, these academic dermatopathologists are humans, science is ever-evolving, and medicine is not always perfectly executed.
This is, of course, my opinion. There are many excellent pathologists and dermatologists reading biopsies and sending the tricky ones out to dermatopathologists. The point is to ask questions if you are concerned. I wanted to explain the process so that you can make your choices based on insider knowledge.
Elmore J.G., Barnhill R.L., et. al., Pathologists’ diagnosis of invasive melanoma and melanocytic proliferations: observer accuracy and reproducibility study, BMJ
2017; 357 doi: https://doi.org/10.1136/bmj.j2813(Published 28 June 2017)