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The designation, micrometastasis, also has been used in a more specific manner to give recognition to discontinuous foci of melanoma in the dermis. In this definition, the lesions should measure more than 0.05 mm in diameter, and should be in the immediate vicinity of a vertical growth component. In factoring the significance of these nests into the prognostic evaluations, they, regardless of size, should be characterized as a modification of clinical stage rather than introduced into the prognostic evaluation by including the micrometastases in the measurement by Breslow’s criteria. Not all micrometastases are at the deep margin of vertical growth components. Often, they are present in the upper portion of the dermis in linear arrays; they are often situated in patterns that would not lend themselves to manipulation by Breslow’s criteria. They are comparable in significance to the finding of invasion of small vessels in the dermis beneath the vertical growth component, but have the added significance of being not only in the lumen of a vessel, but also of having extended beyond the confines of a vessel into the dermis, or adjacent soft tissue; such microscopic foci are incipient satellites.
Agminate “Spitz nevus” is a well documented clinical entity, but the nature of the secondary lesions is not well defined. The phenomena of multiple “Spitz nevi” in a limited locus may be observed in infancy and childhood. In the primary lesion, the patterns may deviate from those of typical “Spitz nevus.” Rounded nests of cells may be more common than fascicles of cells. In addition, the cells in nests tend to have plump, round nuclei. In early examples, the agminate lesions may not be clinically apparent. They are manifested histologically by small clusters of nests of cells in patterns of local satellitosis at the interface between the papillary dermis, and the reticular dermis. Agminate “nevi” of this type may represent local lymphatic metastases. This opinion does not imply that the cells of these lesions would have the capacity to colonize regional lymph nodes. The ability to establish an ecological niche in a lymph node may be of a different order from the ability to manifest local satellitosis in the skin. Small clusters of tumor cells within small, dilated lymphatics are occasionally a feature in the dermis immediately adjacent to the border of a typical “Spitz nevus.”
Summary:
Herein, several arbitrary segments of various melanocytic neoplastic continua have been characterized as “entities.” In the common expressions of common melanocytic neoplastic continua, a precursor has been identified as a two dimensional process at its deepest level, and a melanoma has been identified as a three dimensional lesion at level III or deeper. Nuclear grades and vertical dimensions have been emphasized, and offered as the basis for the delineation of a prognostically favorable borderland between common dysplasia and melanoma; the management of an individual lesion in the borderland is little affected regardless of the manner in which this portion of the borderland has been segmented. All of these common lesions in the borderland would be managed by conservative excision and follow-up. Herein, it is proposed that this portion of the borderland might be characterized as borderline melanocytic neoplasia of indeterminate ( for some of these lesions, the qualifier, insignificant, might even be appropriate) malignant potential. This category could then be qualified as either dysplasia variant, or melanoma variant depending on whether the lesions are basically two dimensional, or three dimensional. With respect to Breslow’s criteria, the upper limit of this borderline category might be defined as 1 mm. For patients with lesions confined to this range, the survival at 5 years would be approximately 90% or greater. This is not the same as saying that an individual patient with a lesion in this range has a 90% chance of survival, if the lesion is properly diagnosed, excised locally, and the patient carefully followed. These figures apply only to predictions when groups of patients are studied.
An appreciation of nuclear grade has a role in the partitioning of this borderland of thin lesions. The dysplasia variants are lesions showing moderately severe to marked atypia (high grade dysplasias). The category would include not only those segments of the borderland that are commonly characterized as “melanoma-in-situ,” but also segments that by custom have been assigned to the category of “melanomas” (including “SSM”) at level II. In regard to the “melanoma” variants in this borderland, the category would include lesions that are three dimensional ( a definition of vertical growth), not arrested in fibrous lamellae (the pattern of arrested variant growth at level III), and measure 1 mm or less. The category would include thin lesions in which nests of cells are arrested in fibrous lamellae (pattern of arrested variant growth at level III). It would embrace the borderline, thin minimal deviation melanoma of Reed, a category which includes SSM, LMM, and ALM showing thin vertical growth (1 mm or less), and either level III or level IV patterns.
The high component of common nevus-like MDM in this group of cases is surprising. It might be taken as evidence that this is a common intermediate stage on the pathway to common melanoma. The fact that many of these thin lesions metastasized is also surprising; an observer might come away with the notion that this form of MDM is somewhat aggressive; there might be an indication for providing prognostic guidelines by common Breslow’s criteria. The explanation for the high component of common nevus-like MDM probably is related to my role as a consultant. Many of the thin lesions in this study had been seen by me as a consultation case. Many of the patients would be referred to Dr. Edward Krementz for treatment. The demographic material was furnished by the registar working in the Surgery Department at Tulane School of Medicine. Some of the lesions were treated in the 1960’s and the treatment included wide local excision and perfusion. Many of these lesions were treated in the 1970’s, and perfusion was not a routine. In my initial interpretation, many of these lesions had been classified many as MDM.
I invite the reader to examine other SECTIONS on this site (www.pathology-skin-rjreed.com). There is a /general index which lists the other sections. The newer additions to this site present discussions of the problem of the “Spitz variants” of melanocytic neoplasia (/spectrumspitz.html, and /juvmelanom.html).
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