Chapter 13: Biopsy and Definitive Excision of Primary Cutaneous Melanomas

BIOPSY

A skin lesion that is suspicious for melanoma is best removed by excisional biopsy with a 1- to 2-mm clinical lateral margin and a deep margin into the subcutaneous fat, underneath all epithelial appendageal structures.¹ This can be performed on most lesions up to 1.5 cm in diameter (Fig. 13-1). The biopsy scar should be oriented to be compatible with a subsequent wide local excision should the lesion prove to be melanoma. On the extremities a longitudinal or oblique incision is preferred. On the trunk or the head and neck the biopsy should be oriented parallel to the skin lines. A full-thickness biopsy should be undertaken in order to accurately interpret the maximum tumor thickness, the presence or absence of ulceration, and the level of invasion.¹

An incisional biopsy using either a 6-mm punch instrument or a scalpel (removing a small fusiform ellipse) may be appropriate for lesions that are large or located at a difficult anatomic site where one would want to know the diagnosis before removing the entire lesion (Fig. 13-1). The biopsy should be taken from the most raised or the most darkly pigmented area, but since it removes only part of the tumor, a repeat biopsy may be necessary if the histological diagnosis does not agree with the clinical impression. An incisional biopsy involves removal of a portion of a skin lesion, in which the lateral margins are incomplete, and therefore, by definition, positive, but the deep margin should be in the subcutaneous fat, underneath all epithelial appendageal structures.² Final determination of the tumor thickness cannot be made until the entire lesion has been excised and examined by the pathologist. For suspicious lesion beneath nailbeds, the biopsy approach is more problematic. Although digital tumors usually arise from the proximal nail fold from which the biopsy must be procured, biopsies of subungual pigmented lesions necessitate splitting of the nail plate.

A shave biopsy involves removal of a portion of a skin lesion for diagnosis, using a scalpel or a sharp razor blade, in which the deep margin of resection is within the dermis. However, if the lesion does prove to be a melanoma, a prior shave biopsy may prevent accurate assessment of Breslow thickness. Shave biopsies may be considered for small flat lesions where the likelihood of melanoma is considered to be low, but are inappropriate when a melanoma is suspected, ...