Mohs excision sets melanoma standard

"Mohs surgery offers the advantages of optimal margin control, high cure rates and tissue conservation. So the question might arise - why don't we do Mohs surgery for every type of skin cancer?" asks John Carucci, M.D., Ph.D., chief of Mohs micrographic and dermatologic surgery at Weill Medical College, Cornell University, New York-Presbyterian Hospital.

In answer to this question, he says some physicians believe potential difficulties exist in recognizing melanoma on frozen sections. Both standard excision and Mohs surgery share the goal of clear margins, Dr. Carucci says.

"Margins for standard excision are based on depth. And high cure rates are achieved with standard excision in many cases," he says.

Dr. Carucci says a potential disadvantage of standard excision is that this method only looks at 1 percent to 3 percent of the true surgical margin when one is examining the excised area via the bread loaf technique.

"This can pose difficulties in select situations, including lentigo maligna," he adds.

In contrast, he cites a landmark study of Mohs surgery using the fresh tissue technique to treat 535 patients with 553 melanomas. Findings showed results - regarding metastasis and five-year survival - comparable to historical controls treated with wide local excision (Zitelli JA, Brown C, Hanusa BH. J Am Acad Dermatol. 1997 Aug;37(2 Pt 1):236-245). The same study showed a local recurrence rate of approximately 0.5 percent.

As to whether melanoma can be detected on frozen sections, Dr. Carucci cites a study in which researchers achieved 90 percent specificity in examining 221 specimens from 59 patients, along with low recurrence rates (Zitelli JA, Moy RL, Abell E. J Am Acad Dermatol. 1991 Jan;24(1):102-106).

However, he says, "Other studies show a diagnostic discrepancy with respect to margin status. When one looks at those studies, one must realize that in order to distinguish melanoma on frozen section, slides must be of extremely high quality."

As for lentigo maligna, he says recurrence rates for standard excision among patients with a history of extensive sun damage can approach 15 percent.

Meeting goals

"In terms of managing melanoma, particularly with a background of extensive sun damage, one wants to accomplish two things - to visualize the greatest possible percentage of the true surgical margin, and to optimize detection of malignant melanocytes," Dr. Carucci notes.

To meet the former goal, he says options include Mohs surgery and modified processing of excisional specimens (an en face technique).

To modify detection of malignant melanocytes, Dr. Carucci adds that if a physician fears he or she will be unable to visualize them on a frozen section, that doctor may choose to use paraffin sections or special histologic stains.

Standard margins for lentigo maligna typically measure 5 mm, in accordance with National Institutes of Health consensus standards for melanoma in situ, he says. However, Dr. Carucci adds that a number of studies have shown that this 5 mm margin is not necessarily always sufficient to achieve a tumor-free plane. In one study, he says researchers using a 6 mm margin cleared only about 50 percent of patients (Zalla MJ et al. Dermatol Surg. 2000 Aug;26(8):771-784).

Staged techniques also can help surgeons visualize margins more effectively, Dr. Carucci adds. For example, he says the square technique involves removing a peripheral strip of 2 mm to 4 mm around the lesion using a double-bladed knife, leaving a central island of tissue that's essentially removed after margins are cleared (Johnson TM, et al. J Am Acad Dermatol. 1997 Nov;37(5 Pt 1):758-764).