ORLANDO – Mohs surgery is an appropriate choice for lentigo maligna patients because advances in immunostaining allow easier and more efficient identification of melanocytes on frozen sections, said Dr. Basil S. Cherpelis.
Recent literature shows the recommended 5-mm margin for melanoma is often inadequate, Dr. Cherpelis said at the Orlando Dermatology Aesthetic and Clinical conference.
The margins needed for successful treatment of lentigo maligna vary – 5 mm is enough for some melanomas, while others might need a 1-cm margin.
"It makes sense to use a method of intraoperative margin control," said Dr. Cherpelis, of the Moffitt Cancer Center at the University of South Florida in Tampa. "That’s what gives you the flexibility to adjust your margins based on the melanoma that you happen to be treating."
One option for intraoperative margin control is traditional frozen sections, Dr. Cherpelis said. But frozen sections offer a limited view of the margin, and they pose the problem of freeze artifacts, which can make the distinction between melanocytes and keratinocytes difficult. A second option is the square or perimeter method, but this method involves a 1-2 week wait for complete results, which is inconvenient for doctors and patients.
A third option is Mohs surgery. Literature shows that Mohs is effective for melanoma, with the benefits of entire visualization and same-day reconstruction, but it is not widely used, Dr. Cherpelis said. One reason: Melanomas on permanent sections have halos around them, making identification easy, but frozen sections have similar halos around keratinocytes and melanocytes.
Using immunostaining as part of Mohs surgery can solve the identification problem, but until recently immunostain protocols could take at least an hour.
Dr. Cherpelis and his colleagues have streamlined the process.
"We have been able to shorten our protocols down to 19 minutes for MART-1 [melanoma-associated antigen recognized by T cells] and 35 minutes for MITF [microphthalmia-associated transcription factor]," Dr. Cherpelis said (Derm. Surg. 2009;35:207-13; Am. J. Dermatopath. 2010; 32:319-25, respectively). The protocols make Mohs surgery easier because the immunostain helps clinicians easily identify melanocytes.
MART-1 (a cytoplasmic stain) is the most common immunostain, but some data suggest it can falsely label keratinocytes in inflamed skin or in pigmented actinic keratoses, Dr. Cherpelis said. It also can cause pseudo-confluence (the appearance of touching melanocytes). By contrast, MITF is a nuclear stain, so it does not have the problem of pseudo-confluence.
Dr. Cherpelis said he had no relevant financial disclosures.