Histologic criteria for diagnosing primary cutaneous malignant melanoma.

Malignant melanoma accounts for the largest number of deaths attributed to skin cancer. It also provides the most diagnostic challenges for the histopathologist. This article, attempts to describe the histologic features most closely associated with the various growth patterns of the most common subtypes of melanoma. While it has been shown repeatedly that histologic subtypes likely provide clinicians and patients with minimal to no prognostic information, it is useful to separate these entities in order to elucidate the varied histologic features seen within the class of tumors known as melanoma. The discussion centers around a checklist of changes seen at the microscope that are associated with this diagnosis. The goal of this chapter is to provide the reader with one perspective on the series of changes that are used in order to establish (or exclude) a diagnosis of melanoma. There is a comprehensive literature that critically evaluates histologic parameters associated with this collection of tumors and relates them to prognostic information, and no attempt will be made to correlate the histologic change with prognostic information. This will be discussed in another chapter in this volume. Similarly, more esoteric subtypes of melanoma are characterized by histologic features that differ from the common types of melanoma and will be addressed in another chapter.