Even Mohs surgeons with ample experience in detecting basal cell and squamous cell carcinomas can have difficulty detecting malignant melanocytes in frozen sections, making many apprehensive about using Mohs surgery for lentigo maligna. But proponents of the technique say the fast results and reduced rate of recurrence make Mohs well worth the effort.
Proponents of the approach argue that even when surgical margins are tweaked for some added assurance, the surgery is still justifiable over alternatives in its ability to cure melanoma in situ.
"With melanoma in situ on the face, you want to conserve as much tissue as possible and create as small a surgical defect as you possibly can, so the idea of having microscopically controlled margins is theoretically very appealing," says Philip LeBoit, M.D., professor of clinical pathology and dermatology at the University of California, San Francisco (UCSF), and co-director of the UCSF Dermatopathology Service.
"But there can be tremendous difficulty in distinguishing between enlarged melanocytes on the edge of a lesion, which can be very scant and hidden between keratinocytes and normal melanocytes, and enlarged but non-neoplastic melanocytes that simply result from chronic sun damage.
"When you look at the face of older patients, in particular, who have a lot of sun damage, they may have more melanocytes per unit area and those melanocytes may be larger, so it could be incredibly difficult, even with permanent sections, to distinguish between the edge of a melanoma and sun-damaged skin," Dr. LeBoit tells Dermatology Times.
Most Mohs surgeons may have great expertise in basal cell and squamous cell carcinomas, but little skill when it comes to melanoma in situ.
"The majority of Mohs surgeons are not nearly as skilled at recognizing melanoma, let alone the very subtle changes in melanoma, as they are at recognizing BCC and SCCs," Dr. LeBoit says.
A small group of highly skilled Mohs surgeons has mastered the art of detecting such changes, but those surgeons are few and far between.
And while there have been advances in rapid immunohistochemistry, which offers a more advanced way of looking at sections using immunoperoxidase staining, those measures still fall short, Dr. LeBoit says.
"A lot of the current markers just don't do a very good job of telling melanoma in situ from actinic melanocytosis. They just show increased melanocytes in sun-damaged skin," he says.
The result is that some who do take on Mohs surgery for melanoma in situ will wind up taking an extra ring of normal tissue in order to err on the side of caution.
"It's kind of a way of using microscopically controlled margins, plus some insurance, but you might say that if you're going to do that, why do the procedure at all?" Dr. LeBoit says.
Roy Grekin, M.D., a dermatologist and colleague of Dr. LeBoit's at UCSF, is among those who take the safer approach of using Mohs, but also taking the standard 5 mm margin. He says the answer is simple: Doctors get immediate results.
"With a lesion on the face, you're frequently going to have to do a flap or a graft on the patient, and if I'm going to do that, I'm anxious to make absolutely sure the area is clear before I move ahead.
"With Mohs, I can accomplish that by getting the answer that day, as opposed to sending the tissue to the lab and possibly finding out a week later that I didn't get it all and having to go back and take everything apart," Dr. Grekin says.
In addition, he says he doesn't feel entirely secure with the results of vertical sections that labs use.
"With a vertical section, the lab will examine less than 1 percent of the peripheral margins, so it's possible that the part they look at is clear, but somewhere in the other 99 percent, there are still areas with melanoma in them, and there is the potential for a recurrence.
"With Mohs, however, you look at 100 percent of the margins, so you're not going to get any sample error, and the risk of inadvertently leaving something behind is much lower," Dr. Grekin says.