Many patients who have had a biopsy for skin cancer ask if it is still necessary to undergo a second procedure for definitive treatment. “It’s healed up,” or “There doesn’t look like there’s anything left” are common thoughts we hear from our patients.
It is important to note that a skin biopsy is a diagnostic, not therapeutic procedure. In other words, a biopsy is meant only to take a small portion of a suspicious growth in order to send it to another doctor – the pathologist – who examines the tissue under the microscope to make a diagnosis. Biopsies are not intended to remove or cure skin cancers.
Although the common sun related skin cancers we see and treat develop in the outer layer of the skin (the epidermis), they not only grow broadly, but also grow deeply into the layers beneath. So while skin biopsies may shave off or remove the visible, outwardly growing portion of a skin cancer, they are not meant to provide clear margins (complete removal) at the edges or underside. Often times, as areas heal after the biopsy, normal skin can grow over the portion of the skin cancer that is left behind, giving the appearance that it has been cured.
This can be misleading, because patients feel that they no longer need treatment, but a portion of skin cancer has now been “trapped” under the skin and can grow significantly before it is detectable. Thus, it is imperative to seek evaluation of your biopsy site and know that, even if the site looks well healed, there is almost certainly residual skin cancer that should be treated.
To make things even more complicated, occasionally a biopsy report may say that the skin cancer was ‘clear in the planes of sectioning’. This does not mean that the skin cancer was completely removed. This is the pathologist’s way of saying “in the piece I saw, it looked like the skin cancer was out. But I didn’t see the whole piece of skin, so I might not be right.” In fact, we know from prior studies that even if the biopsy report says the skin cancer has been removed, there is residual cancer present as often as 25% of the time.
The advantages of Mohs surgery are the ability to precisely remove only the portion of skin that is involved with skin cancer and preserve as much of the normal skin. Your Mohs surgeon acts as both surgeon and pathologist, so he or she is able to remove the visible healed over biopsy site and immediately examine the edges and underside while you wait to ensure it has been completely removed. Think of it as being able to remove a bruise (the cancer) from an otherwise perfectly good apple (your skin!) and keeping as much of the healthy apple behind for you to enjoy.