Surgical Margins for Melanoma in Situ
Using Mohs surgery to delineate the true dimensions of a tumor, researchers identify a better standard for excision.
Excision of melanoma in situ remains more art than science. Those who use conventional excision are prepared for a high rate of local recurrence after standard 5-mm margins, and even after Mohs, some surgeons employ adjuvant therapies along the periphery (e.g., topical imiquimod) to further decrease the risk for recurrence. The 5-mm margin established by a 1992 consensus opinion is understood to be insufficient, but until now, little evidence has been available to set another specific benchmark.
These investigators reviewed 1120 Mohs surgeries performed in 1072 patients with melanoma in situ from 1982 to 2008 at a single center to estimate the appropriate clearance margin needed for conventional (non-Mohs) excision. In each case, the central melanoma in situ was debulked, and successive concentric 3- mm–wide saucers extending through subcutis were removed for frozen section inspection of the lateral and deep margins. To clear the melanomas, 6-mm margins were sufficient in 86% of cases, 9-mm margins cleared 98.9%, 1.2 cm cleared 99.4%, 1.5 cm cleared 99.6%, and 100% of lesions were cleared with 3-cm margins. The 9-mm margins were significantly superior to 6-mm margins (P<0.001). Gender, location, and lesion diameter did not affect these results. Overall, the 10-year recurrence rate was 0.8%. The authors conclude that 9-mm margins, rather than the traditional 5-mm margins, are appropriate for melanoma in situ excision.
Comment: This study is a major contribution to the establishment of standard margins for excision of melanoma in situ. The authors work from the reasonable conceit that Mohs surgery with repeated narrow margins can be used to estimate the true extent of a tumor. Operating from this logic, the researchers showed that 9-mm margins (i.e., 3 consecutive 3-mm "stages") were far superior to 6-mm margins (2 consecutive 3-mm stages). The difference in clearance was not only statistically significant but also very clinically significant: The slightly larger margin was associated with a recurrence rate less than one-tenth the rate with the smaller margin. This is a single-center study, and more confirmatory studies may be required to generalize the result and alter the standard of care. On the other hand, the conclusions are intriguing given the extraordinarily large cohort and the high quality of the Mohs practice that produced the data, as evidenced by the extremely low recurrence rate.
Published in Journal Watch Dermatology April 6, 2012
Kunishige JH et al. Surgical margins for melanoma in situ. J Am Acad Dermatol 2012 Mar; 66:438.
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