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Expert Critique
FROM THE ASCO Reading Room
Although use of the technique of MMS for MIS has slightly improved in recent years, nearly all lesions (90%) are still treated with WLE. This is because there is still a lack of reliability in detecting atypical melanocytes in MMS frozen tissues and many surgeons are not aware of the available data for supporting MMS as a good alternative to WLE. MMS is more appropriate for ill-defined skin cancer lesions such as MIS on sun-damaged skin.
In the past there has been a lack of any studies or trials comparing MIS and WLE, but a newly published retrospective study included 662 MIS patients treated with MMS or WLE from 1978 to 2013. The overall recurrence rate was 1.8% with MMS and 5.7% with WLE, and the 5-year overall survival rate was 92% for MMS and 94% for WLE. The study showed that there was no statistical significance between MMS and WLE. The researchers determined that further prospective and randomized study trials need to be done to assess the cosmetic differences and adverse outcomes of MMS versus WLE.
Surgery is the current recommended treatment for patients with melanoma in situ. The most common surgery is wide local excision -- i.e., removal of the tumor along with a margin of normal-appearing skin of 0.5 to 1 cm. After removal, the surgical defect is closed by suturing, and the removed tissue is sent for microscopic evaluation to assess if the tumor is completely removed. The microscopic examination, however, entails looking at only a small fraction of the surgical margin.
In an interview, Maria L. Wei, MD, PhD, director of the Dermatology Genetics Clinic of the University of California, San Francisco, explained that in certain situations, this method can be problematic, because the surgical wound is closed before it is known if the tumor is cleared. "On the head and neck, and other sites, often complex closures are performed to accommodate nearby vital structures -- i.e., the eyes, nose, and mouth. If a surgical margin returns as positive for tumor, it is difficult to pinpoint where along the complex suture line there is remaining tumor.
"In addition, the of normal-looking skin can be difficult on the head and neck due to the presence of vital structures that would ideally be preserved for functional and cosmetic purposes," she said.
An alternative surgical technique is Mohs micrographic surgery (MMS), which allows examination of the entire surgical margin during the procedure and allows clearance of the tumor before surgical repair. MMS theoretically can preserve tissue, enabling clearance of tumor to be determined without the necessity of obtaining the 0.5 to 1 cm margin of normal tissue, Wei noted.
MMS is now used to treat a growing subset of individuals with MIS, she continued. During MMS, unlike wide local excision (WLE), the entire cutaneous surgical margin is evaluated intraoperatively for tumor cells. MMS may be better suited for removal of ill-defined skin cancers such as , which make up about 80% of these tumors, she said.
Her team conducted the first study to directly compare outcomes for these two types of surgical treatments: "Previous studies looked separately at either Mohs outcomes or WLE outcomes. Review papers that have compared WLE and Mohs outcomes were comparing results from completely separate institutions, using different methods, and different patient population-selection criteria. Thus, the results are not directly comparable," Wei said.
The researchers conducted a of 662 patients with melanoma in situ treated with MMS or WLE per the standard of care in dermatology and surgery (general surgery, otolaryngology, plastics, oculoplastics, or surgical oncology) at an academic tertiary care referral center from 1978 to 2013, with follow-up through 2015.
The cohort consisted of 277 patients treated with MMS, mean age of 64, and 385 patients treated with WLE, mean age of 58.5. Median follow-up was 8.6 years.
MMS was used more frequently on the face (80.2%) compared with WLE (36.7%). For patients with melanomas of the scalp and neck, 8.3% received MMS and 6.8% WLE.
The overall recurrence rates were 1.8% in the MMS group, compared with 5.7% in the WLE group. The mean time to recurrence was 3.91 years after MMS and 4.45 years after WLE.
The 5-year recurrence rate was 1.1% in the MMS cohort compared with 4.1% in the WLE cohort. The calculated 10- and 15-year recurrence rates for MMS treatment were 1.8% and 5%, respectively. For WLE treatment, the 10- and 15-year recurrence rates were 6.8% and 7.3%, respectively.
The surgical margin taken for WLE-treated tumors was greater for recurring versus non-recurring tumors.
The 5-year overall survival rates were 92% for the MMS group and 94% for the WLE group. Two patients in the MMS cohort and 13 in the WLE cohort died of melanoma, with a mean time to death due to melanoma of 6.5 years in the MMS cohort and 6.1 years in the WLE cohort.
"For melanoma in situ, there is no difference in outcomes -- as measured by recurrence rate, melanoma-specific survival, and overall survival -- for patients treated with Mohs compared with those treated with WLE," Wei said. "There is a suggestion that the outcomes are better in Mohs, but the data were not statistically significant."
MMS has advantages in melanoma patients, including clearance of tumor before surgical repair, and tissue preservation and a smaller scar in some cases. The disadvantage of Mohs is the longer time to conduct the procedure, she said.
"The better candidates for Mohs micrographic surgery are patients with melanoma in situ on anatomic sites, such as the head and neck, hands, and feet, where the clearance of tumor is ideal before surgical repair and where preservation of the function and cosmesis of anatomic structures is desired."
She noted that the present study is a direct comparison of the two methods using retrospective data, and that a prospective study is needed to assess whether there are functional or perceived cosmetic differences or adverse outcomes for patients treated with MMS versus WLE.
"As current practice stands, for melanoma in situ on the head and neck and hands and feet, Mohs micrographic surgery is an excellent option."
Wei reported having no relevant financial disclosures.