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.
Journal Watch © 2012 Massachusetts Medical Society