Melanoma In Situ: A Critical Review and Re-Evaluation of Current Excision Margin Recommendations

Most international clinical guidelines recommend 5-10 mm clinical margins for excision of melanoma in situ (MIS). While the evidence supporting this is weak, these guidelines are generally consistent. However, as a result of the high incidence of subclinical extension of MIS, especially of the lentigo maligna (LM) subtype, wider margins will often be needed to achieve complete histologic clearance. In this review, we assessed all available contemporary evidence on clearance margins for MIS. No randomized trials were identified and the 31 non-randomized studies were largely retrospective reviews of single-surgeon or single-institution experiences using Mohs micrographic surgery (MMS) for LM or staged excision (SE) for treatment of MIS on the head/neck and/or LM specifically. The available data challenge the adequacy of current international guidelines as they consistently demonstrate the need for clinical margins > 5 mm and often > 10 mm. For LM, any MIS on the head/neck, and/or ≥ 3 cm in diameter, all may require wider clinical margins because of the higher likelihood of subclinical spread. Histologic clearance should be confirmed prior to undertaking complex reconstruction. However, it is not clear whether wider margins are necessary for all MIS subtypes. Indeed, it seems that this is unlikely to be the case. Until optimal surgical margins can be better defined in a randomized trial setting, ideally controlling for MIS subtype and including correlation with histologic excision margins, techniques such as preliminary border mapping of large, ill-defined lesions and, most importantly, sound clinical judgement will be needed when planning surgical clearance margins for the treatment of MIS.