SAN DIEGO – Mohs surgery has a place in the treatment of melanoma in situ and invasive melanoma, “but in my practice it doesn’t have a place every day,” Dr. Michael H. Swann said at a melanoma update sponsored by the Scripps Clinic.
Dr. Swann, who performs Mohs surgery in a Springfield, Missouri–based dermatology practice 4-5 days per week, said that one of the main benefits of the technique for melanoma is that the recurrence rates are favorable to matched paraffin controls, a finding reported in a 1997 study of 533 patients. That study found that to achieve clear margins in 83% of patients, a 6-mm margin was required, 95% of tumors cleared with a 9-mm margin, and 99% of tumors cleared with a 16-mm margin (J. Am. Acad. Dermatol. 1997;37:236-45).
“So when we think about things that are left behind with local disease, these numbers stick in my head when I treat patients and I think about how I’m going to treat these tumors,” Dr. Swann said. “The way to treat melanoma is to detect it early and to get all the cells out surgically if you can.”
Other benefits of using Mohs surgery for melanoma are that the margin evaluation is superior to other techniques, it spares normal tissue, and immunostains are readily available for difficult cases. “You can turn around the tissue in about 40 minutes now, but immunostains by themselves are not the answer,” Dr. Swann commented. “There are plenty of Mohs surgeons like myself who don’t use immunostains, because for the most part, immunostains are used by labs to make the diagnosis of melanoma. The margins of these melanomas are seldom immunostained because the diagnosis is not in question.”
The convenience of a single-day procedure is another benefit of using Mohs surgery for melanoma, especially in geographic locations such as Missouri, where many patients live in rural areas. “It takes some patients 3 or 4 hours to drive to our practice,” Dr. Swann explained. “For them to come back 3-4 weeks in a row every 3 or 4 days to have a little more melanoma in situ taken off the edge would be inconvenient. It may make the patient decide not to treat the tumor at all. Mohs is convenient.”
Mohs surgery also has its share of drawbacks, Dr. Swann said. One is the fact that frozen sections can be difficult to interpret. “You have to have an excellent histotechnician and a surgeon who has experience with the slides,” he said. “The melanocytes are sometimes too subtle to distinguish from keratinocytes. This is particularly evident if you have freeze artifact.”
Other limitations of Mohs, he said, include the fact that the cytology is not always readable and that melanocytic hyperplasia in sun-damaged skin “is very difficult to pick out from melanoma in situ, particularly lentigo maligna.”
Another shortcoming is that immunostains are not available from all histopathology labs. “Occasionally we’ll get missing epidermis, especially if the technician is not excellent,” he said.
Dr. Swann instructs his patients to avoid sun exposure several weeks before surgery or biopsies, and emphasized that having a good supportive relationship with a pathologist “is always in the patient’s best interest.”
One alternative to Mohs micrographic surgery is slow Mohs, whereby paraffin-embedded tangential sections of tissue are submitted for 100% margin evaluation. Dr. Swann described this technique as “a coordination of a laboratory and the Mohs surgeon working as seamlessly as possible to treat these patients.” These fast-turnaround paraffin-embedded pathology specimens, known as “rushed perms,” take 24 hours in the best situation, “usually 2-3 days,” Dr. Swann added. “It’s not the easiest process. That’s why we use the same histopathology lab over and over to do our work.”
Turnaround time for hematoxylin and eosin stain is 24-72 hours and immunostains usually add 24 hours.
Other alternatives to Mohs surgery include wide local excision and en face sections via geometric serial excisions.
Dr. Swann had no conflicts to disclose.