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MDM of Spitz-like type (i.e., MDM of juvenile melanoma type) is a controversial neoplasm. Atypia in the setting of a Spitz nevus-like lesion has been, and is, a confusing aspect. For years, many observers have simply accepted atypia as a part of the pattern of “Spitz nevus.” This failure to assign significance to cytoloic, and histologic atypia has been called into question as more and more examples of “Spitz nevi” have found their way into the courts following claims of malpractice. A typical vertical growth component in the setting of a Spitz-like variant seems to be one of the more constant features of Spitz-like lesions that metastasize to regional lymph nodes (c25t3P1-6 & c26t3P1-6 . Patterns of variant and migrant vertical growth are intrinsic to the virtual images of classic “Spitz nevus;” such patterns in combination with atypia and mitotic activity are worrisome, but the assignment of a lesion showing this combination of features to the MDM category requires a troublesome extension of criteria. Such lesions probably are best designated Spitz-like MDM’s of indeterminate malignant potential, or as melanocytic neoplasia of Spitz-like type (indeterminate malignant potential, variant and migrant vertical growth-like patterns). Such lesions might be additionally qualified as to degree of atypia and mitotic activity.
Vertical growth has been slighted as a significant parameter. Many observers regularly measure the “thickness” of a lesion without acknowledging the relationship between vertical growth and Breslow’s criteria.They go to lengths to avoid the designation, vertical growth. In part, the emphasis on melanoma-in-situ has clouded the significance of vertical growth in the recognition of melanocytic lesions with the capacity for metastasis. Patterns of variant and typical vertical growth are represented in c27t3P1-6.
The dermal patterns of a nevus-like MDM may mimic the patterns of a common dermal nevus. In this category, the cells in the dermal component tend to be rounded, and show disarmingly bland cytologic features (c28t3P1-8). Some examples might be assigned to the category of “ancient nevus,” but a major proponent of this type of assignment has retracted his support of the designation, outside the basic patterns of a cellular blue nevus.
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