Margin Assessment of Cutaneous Melanoma

Guidelines for Melanoma Margins

When the goal is to remove a primary melanoma surgically, the question arises how widely around the clinically visible lesion or biopsy site should the excision margin be drawn to ensure complete removal of the tumor (in practical terms a histopathologically confirmed negative margin). For some melanomas (e.g., discrete pigmented lesion) there is a good correlation between the clinical and microscopic margin assessment. For other melanomas, however, there is subclinical (clinically invisible or poorly visible, but microscopically confirmed) extension of the tumor in the horizontal plane beyond the area of skin clinically thought to represent melanoma.

Guidelines have been proposed for surgical margins based on historic practice, some published data on the subject, and consensus among clinicians selected to serve on panels. These guidelines have varied over the years. There has been a general trend toward narrower margins for melanoma as it has become apparent, for example, that wide excisions with 5-cm margins for invasive melanoma do not offer any advantage over a 1- or 2-cm margin for survival or risk for local recurrence. Furthermore, for 1- to 2-mm thick primary melanomas, a 1-cm margin often seems to suffice. On the other hand, for melanoma in situ it has also become apparent that some lesions, in particular lentigo malignas, not uncommonly require a 7- to 10-mm or occasionally even wider clinical margin for successful clearance ( Table 33.1 ).

With regard to guidelines, a few comments are in order. First, the margin metrics reflect clinical ( Figs. 33.1 and 33.2 ), not histopathologic, measurements ( Fig. 33.3 ). Second, the purpose of the guidelines of clinical margins is to suggest a rim of tissue for a given melanoma thickness that will achieve a final histopathologically confirmed negative margin at a high probability. It is not the goal or clinically necessary that the tumor be surrounded by a clearance of 5 mm or more of pathologically confirmed normal tissue. For example, when a melanoma in situ has been excised with a clinical measurement of 5 mm and there is a rim of normal skin throughout the periphery of the excision specimen, the surgical margin should be classified as negative and adequate, even if the histopathologic clearance is less than 5 mm, which is often the case, especially when residual melanoma in situ is present ( Fig. 33.4 ).

The purpose of the guidelines is that following them will often yield a negative margin ( Fig. 33.5 ). Sometimes, however, there is such a broad subclinical extent that the margin is unexpectedly positive or too narrow ( Fig. 33.6 ). If the clinical goal was to remove the tumor with a negative margin, and additional tissue can be taken with limited or no extra morbidity to the patient, an additional surgical procedure is then in order to achieve that goal. Not uncommonly, following the margin guidelines will yield an unnecessarily wide clearance, and in retrospect one wonders whether a smaller excision would not have sufficed ( Fig. 33.7 ).

Second, guidelines are guidelines, not mandates. They apply to most but not all lesions or clinical and personal circumstances. Compromises may need to be made to balance the goal of a negative margin with the goal of minimizing morbidity and maximizing quality of life.

Tissue Processing and Margin Review

Whether or not a melanoma has been entirely removed is assessed by microscopic review of an excision specimen. A margin is determined negative if there is only normal tissue and no tumor seen at the outermost rim of the surgical excision specimen (side and deep margin in a two-dimensional view). The accuracy of the margin assessment depends on adequate orientation, processing, and competent microscopic review of the tissue.