FIGURE 1: DIAGRAMATIC REPRESENTATION OF NEOPLASIA IN A MODEL MELANOCYTIC SYSTEM
In this diagram, precursor lesions, either premalignant melanocytic dysplasias or radial growth components, are represented as a plane and vertical growth components are represented as components of the cone.
The plane has 5 domains, including an indeterminant category, and mild, moderate, moderately severe, and marked categories (i.e., domains). The likelihood for a lesion to enter vertical growth is proportional to the degree of dysplasia. The width of each segment is proportional to the prevalence of lesions in each of the domains along the plane; there are more mild dysplasias than marked dysplasias. On the other hand, the cross-sectional diameter of the cone is proportional to the age of the lesion in vertical growth. The greater the diameter, the older the lesion in respect to the development of the vertical growth component. The transition from dysplasia may occur even in the domain of the moderate dysplasias.
The pattern of the common final pathway, as manifested in the radial growth component of a fully evolved superficial spreading melanoma, is not a requisite for the emergence of a vertical growth component. A lesion which enters vertical growth before it manifests features of the common final pathway (i.e., marked dysplasia; the last thin segment leading into the cone) is likely to be cytologically bland in vertical growth and thin in its vertical dimensions; it is a minimal deviation melanoma.
The domains along the horizontal axis of the cone are confined by boundaries at 1 mm and 1.5 mm. The domain defined by the boundary at 1 mm defines a special category of thin melanomas. These lesions qualify as borderline melanocytic neoplasia of indeterminant malignant potential. The domain defined by the second boundary includes the intermediate lesions and most lesions in the category will be lesions in various ages of vertical growth. These lesions qualify as intermediate melanocytic neoplasias of indeterminant malignant potential. Beyond the boundary at 1.5 mm, the lesions qualify as real melanomas.
In this approach, there is provision for melanomas (i.e., lesions in vertical growth) to be deceptively bland. The impact of the size of a vertical growth component on therapeutic recommendations is given recognition in the two special categories of dimensionalities (the segment of the cone composed of lesions less than 1mm in vertical dimensions and the segment composed of lesions measuring 1 to 1.5 mm in vertical dimensions); lesions in the two special categories are generally managed by conservative local excision; the prognostic parameters cannot be relied on to identify lesions with the potential for metastases. They identify a large group of lesions that are unlikely to metastasize.
Melanocytomas (Spitz and pigmented spindle cell) are not represented in the plane (Fig. 1), but patterns in the epidermis and papillary dermis of atypical melanocytomas can be related to the plane of the diagram.
For the special melanomas (MDM and desmoplastic or neurotropic melanomas), dimensionalities and their relevance to recommendations for treatment require modifications of boundaries along the cone .
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