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Richard J. Reed, M.D.
March, 2004
New Orleans, LA 70125
rjrpjrlr@aol.com
Minimal Deviation Melanoma and Patterns of Typical Vertical Growth:
In the diagnosis of melanoma, clinical patterns have prognostic significance. Lesions which are flat along the skin surface (regardless of surface diameter) generally have a good prognosis (some spindle cell melanomas in vertical growth can be an exception; such lesions may enter VG by extending early on into the reticular dermis; the papillary dermis may not be significantly expanded). A tumoral component, which is expansile and raised above the surface of the skin, has an association with metastases (hence, the utility of Breslow’s criteria). These clinical observations can be, and in the 1960’s were, correlated with histologic features.
Examination of a histologic section offers a variety of prognostic parameters. On a histologic section, a tumoral component - if ancillary features are of an appropriate type - can be characterized as vertical growth. The tumoral component, being actually a 3 dimensional lesion, has only 2 dimensions on a histologic section; for an appreciation of the dimensionality of a nodule on a histologic section, the imposition of virtual images is required.
Vertical growth can be divided into at least four categories depending on nesting patterns, and on the relationships between nests of tumor cells, and both tumor stroma and the anatomic boundaries of the dermis:
1. Typical vertical growth usually is an expansile nodule (a plaque is an optional variation) in which nests of atypical cells are closely spaced in a delicate fibrous matrix, the character of which resembles an expanded papillary dermis. The nodule, in the absence of other expressions of vertical growth, is confined to a widened papillary dermis. Generally, in common melanomas in typical vertical growth, the tumor, at its interface with the reticular dermis, is outlined by a thin band of inflamed, reactive fibrous tissue.
2. Variant vertical growth is more likely to be a plaque of tumor cells rather than a symmetrically rounded nodule. In variant vertical growth, the nests of tumor cells are loosely, but regularly, spaced in a widened papillary dermis (the nests are not back to back). High grade cytologic atypia is less regularly a feature of variant growth components than of typical vertical growth components. This distinction might be cited as evidence that variant vertical growth is a lower grade of neoplasia than the usual typical vertical growth component. Often, in a thin variant vertical growth component, the dermal component is stratified by degree of cytologic atypia with the least atypical cells being the deepest in the vertical growth component. Often, in thin variant vertical growth components, the nests of cells in the dermal component are entrapped in a dense (often laminated) fibrous matrix; this variation in patterns might be characterized as arrested variant vertical growth. Sclerosing entrapment of nests of tumor cells in this manner may be as much a function of the tumor cells as a response to a host immune response. It may allow for survival of cells, which otherwise are ill-prepared to survive outside an epidermal domain. If, in such a lesion, nevus cells are represented at the interface between the papillary dermis and the reticular demris, they generally are supported by a delicate fibrous matrix, and are beyond the area of sclerosis. Variant vertical growth, particularly as a manifestation of thin lesions showing the pattern of arrested growth, is not as regularly associated with metastases as would be a typical vertical growth component of equal vertical dimensions.
3. Migrant vertical growth is a variation which is associated with either typical, or variant vertical growth. If the lesion shows a component of typical vertical growth, but individual cells or nests and fascicles of cells infiltrate the reticular dermis among collagen bundles, then the component in the reticular dermis is a migrant vertical growth component. Often the migrant vertical growth component will be associated with less inflammation than the remnant of the typical vertical growth component. Migrant vertical growth is likely to be associated with vascular or nerve invasion. These same guidelines apply for the recognition of migrant vertical growth in association with variant vertical growth patterns. Some lesions may show a relatively pure migrant pattern; this is particularly true of some spindle cell (i.e., lentiginous) variants.
4. Desmoplastic variant vertical growth is a variant of migrant vertical growth. It is distinguished by a tendency for the infiltrating cells to induce a sclerotic stromal response. Neurotropic vertical growth is closely akin to migrant vertical growth.
It should be noted that these definitions of vertical growth tend to supplant Clark’s levels of invasion. There are occasional lesions, that can be qualified as a level IV pattern but, lacking a sufficient representation of nests of cells, cannot be characterized as being in vertical growth.
Patterns of typical vertical growth are basic to a definition of classic minimal deviation melanomas (MDM). Migrant patterns in association with a typical component are common. A variant vertical growth component is more difficult to accommodate in the category of MDM. A pattern of typical vertical growth in the setting of a Spitz-like lesion, should be viewed with suspicion; MDM of Spitz-like type generally is charaterized by patterns of typical and variant vertical growth. In this section, the histologic patterns of premalignant melanocytic dysplasia and early (young) melanomas are discussed. The patterns, thus established, form the basis for the recognition of vertical growth in a Spitz-like lesion.
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