MAUI, HAWAII – "Slow Mohs" has gained near-universal acceptance among skin cancer specialists as a definitive surgical technique for complete removal of lentigo maligna melanoma while simultaneously sparing normal tissue, according to Dr. Ellen Marmur of Mount Sinai School of Medicine, New York.
The big advantage that slow Mohs has over standard wide local excision with 0.5- to 1-cm margins is a 5-year cure rate approaching 100%. In contrast, standard excision has a recurrence rate of up to 20%, she said at the Hawaii Dermatology Seminar, sponsored by Global Academy for Medical Education/Skin Disease Education Foundation.
Slow Mohs is a modified form of Mohs micrographic surgery. The surgery compares with conventional Mohs: It is staged, margin-controlled excision. But in slow Mohs, rush permanent sections are sent off to the pathologist rather than the frozen sections integral to conventional Mohs.
Dr. Marmur relies upon slow Mohs, with "bread-loafing" of the central tumor by the pathologist, because the permanent sections better preserve the tumor’s microscopic features. Interpreting atypical melanocytes in frozen sections can be quite a challenge. However, she added, some Mohs surgeons have found that using rapid immunostains also markedly improves the sensitivity and specificity of frozen sections in lentigo maligna surgery.
Slow Mohs takes place over the course of days, she said. "Basically, you do your Wood’s lamp to define the lesion diameter, you measure out your margins, you excise the tumor, pack the area with a bandage, and send the patient home. You rush your pathology, and you don’t do any reconstruction until you get the margins clear."
A pathology report that comes back stating narrow margins are present is "a heart stopper," she added.
"You have the option of observing the area if the margin is clear but the tumor was close to the margin. That’s a good approach for an elderly patient or when the lentigo maligna was in a cosmetically important area."
Lentigo maligna melanoma accounts for 4% of all cases of melanoma. It typically arises on sun-damaged skin in individuals in their 70s or older. Common sites include the malar area, forehead, nose, and temple. The differential diagnosis includes seborrheic keratosis, pigmented actinic keratosis, and pigmented nevus.
Lentigo maligna becomes lentigo maligna melanoma when malignant melanoma cells invade the dermis and deeper appendages. Roughly 5% of lentigo malignas eventually progress to invasive melanoma, according to Dr. Marmur. Typically, a lentigo maligna undergoes extended gradual horizontal growth before beginning a vertical growth phase.
"It spreads like an oil slick for many years," Dr. Marmur said at the seminar.
Established treatment modalities for patients who aren’t surgical candidates include cryotherapy, radiotherapy, and topical imiquimod 5%. All have disadvantages, including high 5-year recurrence rates.
Dr. Marmur noted that a newer nonsurgical therapy drawing considerable interest involves off-label use of topical combination therapy with imiquimod and tazarotene gel. The concept is to use the topical retinoid to disrupt the stratum corneum in order to enhance imiquimod penetration, thereby achieving a greater inflammatory response than possible with imiquimod alone.
Initial data have been published by researchers at the University of Utah, Salt Lake City. They randomized 90 patients with 91 lentigo malignas to imiquimod 5% cream applied 5 days per week for 3 months or to the imiquimod regimen plus tazarotene 0.1% gel on the other 2 days per week. After 3 months of topical therapy, patients underwent conservative staged excision with frozen section analysis with Melan A immunostaining to confirm negative margins.
Of those treated with dual topical therapy for 3 months, 29 of 37 lesions (78%) had complete responses with no residual lentigo maligna at the time of staged excision. So did 27 of 42 (64%) treated with imiquimod alone (Arch. Dermatol. 2012;148:592-6).
The modest difference in outcome was not significant (P = .17). Nevertheless, the Utah investigators wrote that topical pretreatment appears to reduce surgical defect sizes, an important consideration in lentigo maligna because the lesions are often large and located on cosmetically sensitive facial sites. At the patient’s first visit, the researchers saucerize the entire tumor to remove all visible evidence of lentigo maligna and nip in the bud any invasive element that might be present. One month later, after the wound has healed by secondary intention, the patient begins topical imiquimod therapy 5 days per week. If no inflammation is observed, tazarotene gel is added on the other 2 days per week. After 3 months of topical therapy, the patient goes off treatment for 2 months so the inflammatory response can subside. Then a staged excision is performed with 2-mm margins around the perimeter of the original tumor outline.