Mohs technique effective for removing superficial melanoma

Key Points

Birmingham, Ala. - The Mohs technique is as sensitive in picking up melanoma cells as the conventional vertical bread-loafing technique in the management of superficial melanoma, according to a new, small study.

"Mohs technique does not take a 10 mm margin around every tumor, so it is tissue-sparing," says the study's senior author Christopher B. Harmon, M.D., a Mohs surgeon, here.

Superficial melanoma, less than 1 mm and including melanoma in situ, is one of the most challenging lesions Mohs surgeons treat.

"The challenges are how best to remove these tumors in order to get completely clear margins around them, as well as how to spare as much uninvolved or normal tissue as possible."

Narrower margins, broader efficacy?

While melanomas used to be treated with wide surgical margins, newer research suggests that narrower margins are equally effective in the treatment superficial melanoma.

"In the last 10 years, we have developed reliable data that superficial melanoma treated with Mohs micrographic surgery provides the highest cure rate and greatest amount of tissue sparing," Dr. Harmon tells Dermatology Times.

"The difficulty in treating melanoma with Mohs lies in the fact that Mohs sections rely upon frozen tissue sections. Frozen tissue sections do not always allow you to see single cells of melanoma clearly, so many surgeons use the Mohs technique to clear groups of melanoma cells, or thèques. Once the thèques have been cleared, we will then use a permanent section to be sure that all the single melanoma cells have also been removed."

The issue becomes how to process that final layer of tissue for permanent sections. The question is: Is it best for the Mohs surgeon to cut it vertically with the conventional bread-loafing technique or cut the tissue for permanent section in a horizontal fashion, such as that used to take the Mohs layers?

Vertical slicing not superior

Dr. Harmon and colleagues randomly compared the techniques in 23 subjects being treated for superficial melanoma.

The physicians performed vertical or bread-loafing sections in the permanent layer in 12 subjects and did Mohs or horizontal section in 11 subjects.

In the patients being treated with Mohs, surgeons took a 5 mm margin around the clinical lesions and made Mohs sections from those specimens. If the Mohs sections were clear - without thèques of melanoma - surgeons took another 5 mm for permanent horizontal sections. In the bread-loafing arm, they simply went out 10 mm beyond the clinical lesions.

"Ultimately we were comparing our rates of positivity at the same point: 10 mm away," Dr. Harmon says.

The researchers compared rates of positivity between the two arms and found them to be statistically the same.

The small study, according to Dr. Harmon says, suggests that the Mohs technique is just as sensitive in picking up melanoma cells as is the conventional bread-loafing technique.

"The fact that the positivity rates are the same confirms what we know from experience that the Mohs technique is effective at managing this kind of melanoma," he says. "As we make the series larger, my hypothesis is that we will have a higher rate of positivity in the Mohs arm because we are looking at 100 percent of the margin in that arm. In the bread-loafing arm, we are only looking at a small percentage of the true margin."

The goal, he says, is to maximize tissue sparing without compromising tumor removal, cure rate or control of local disease.

Dermatopathology caveat

On a side note, Dr. Harmon says that one of the difficulties from the dermatopathologist's perspective is that when doctors do permanent horizontal sections or permanent Mohs sections, they are being asked to make a call about whether a tumor is benign or malignant based on a snapshot.

With vertical sections, they have the luxury of following the transition of cells from malignant to sun damaged and atypical, yet benign.

"Even though, in that one snapshot view, they may not be definitely positive, there is a tendency to interpret any questionable cells as positive so as not to under-read the slides," Dr. Harmon says.

Disclosure: Dr. Harmon reports no relevant financial disclosures.