Surgical excision margins for melanoma in situ.

INTRODUCTION: Melanoma in situ (MIS) is a non-invasive lesion accounting for up to 27% of all melanomas by Coory et al. (2006).(1) MIS may be a precursor to invasive disease. The Lentigo Maligna (LM) subgroup of MIS carries upto a 4.7% lifetime risk of developing an invasive component by Agarwal-Antal et al. (2002).(2) Surgical excision is recommended however other modalities of treatments are possible. In this study we aim to assess whether histological margins following excision of in situ melanoma has any bearing on recurrence or progression to malignancy.

METHOD: We retrospectively reviewed data accumulated on all melanomas referred to the hospital between the dates of February 2001 to February 2009. We identified all patients with melanoma in situ and for these patients recorded age, sex, anatomical site of lesion, histological type, histological excision margin, recurrence after excision and transformation to malignant melanoma.

RESULTS: A total of 2121 patents were identified having been diagnosed and treated for melanoma of which 192 cases were identified with melanoma in situ representing 9.1% of all melanomas treated. 38% of all the lesions were of the LM subgroup. We noted a higher incomplete excision rate in this subgroup (p < 0.01) compared to the non-LM subgroup. We only noted two recurrences following complete excision (1.1%) and one recurrence in lesions completely excised with histological margins less than 2 mm (1.4%). Both of the lesions that recurred following complete excision were LM lesions. Recurrence following complete excision of LM was 2.9%.

CONCLUSION: Our data suggests that MIS lesions that were not LM and adequately excised even with narrow margins are unlikely to recur therefore reducing the need for wider excision. LM however poses a more challenging clinical problem not only with the higher inadequate primary excision and higher recurrence rates following excision but also the fact that it occurs in much older patients who may be less able to tolerate more extensive surgery. In keeping with the literature we would suggest treating LM lesions more aggressively if possible.