Histologic evaluation of lentigo maligna with permanent sections: implications regarding current guidelines

Obtaining clear margins of resection of lentigo maligna (LM), a subtype of melanoma in situ, from sun-damaged skin of the head and neck continues to be a surgical challenge. The margins may be uncertain both clinically and histologically, causing difficulty in determining the surgical excision perimeter.

We sought to determine whether the current National Institutes of Health consensus conference (1992) recommendation of 5-mm margins is adequate for the removal of LM and to evaluate at what stage tumor-free margins are ultimately attained by using polygonal, staged excisions.

Ninety-two cases of LM were evaluated and treated in a university tertiary care setting. Straight-edge polygonal resections in a staged fashion of LM variants of MIS were evaluated by means of permanent serial histopathologic sections. Each stage of resection used a 5-mm margin. Specimens were color-coded and mapped. Any sites of tumor at resected margins were identified by a dermatopathologist and noted on the map of the excised specimen. Positive margins and areas with markedly atypical melanocytes were further resected, color-coded, mapped, and evaluated as previously described until margins free of tumor were attained.

The patient distribution was 37% female and 63% male, with ages ranging from 24 to 100 years (median age, 70 years). Sixty-nine patients had a biopsy-proven diagnosis of LM involving the head and neck (75%), and 23 patients (25%) had LM elsewhere. Thirty-nine patients (42%) were tumor-free after one stage, 25 (27%) required 2 stages, 14 (15%) required 3 stages, 6 (7%) required 4 stages, and 8 (9%) needed 5 or more stages to achieve tumor-free margins. The central portion of the submitted polygonal excisions revealed an invasive component in 16% of cases.

Use of polygonal perimeter excisions with serial histopathologic permanent sections in a staged fashion is an accurate and thorough method of evaluating and treating LM. This study demonstrates that the standard recommendation of 5-mm margins is adequate in less than 50% of cases and reiterates the need for the careful evaluation of peripheral margins in LM. Because an invasive component can be present and would alter recommended surgical depths and margins, all of the tumor should be submitted at the first stage rather than peripheral margins only.