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The category of Minimal Deviation Melanoma (see EXTERNAL LINK “MDMHALO,” in margin to left) basically embraces melanocytic lesions in which the following requisites are fulfilled: 1.) a component with a vertical growth
(VG) -like pattern (ideally the pattern would be that of a typical VG pattern but some examples are manifested in variant VG patterns) is represented; 2.) if a precursor pattern is represented, there is cytologic
disparity when patterns in the precursor are compared with those of the vertical growth component; and 3.) the patterns in vertical growths, as parcels of virtual images, deviate sufficiently from those of
common melanomas to raise questions regarding both the biologic potential of the lesion in question, and the relevance of prognostic parameters.
With the above definitions as a guide, the category can be expanded to include lesions in which the patterns of precursors (i.e., markers for earlier stages in neoplastic
progressions) lead an observer to the suspicion that the lesion may represent neoplastic progression in a variant nevus. The variant nevi include: 1.) halo nevus variants, 2.) Spitz nevus variants, 3.) pigmented
spindle cell variants (including blue nevus variants), 4.) nevocytic variants, including giant congenital nevi (here, pure dermal dysplasias without evidence of an origin from a lentiginous and junctional component
find a home), and 5.) combined nevus variants. The assignment of a lesion to the minimal deviation category does not in turn validate Breslow’s criteria as a guide to prognosis and treatment. In fact, the biologic
potentials of many of these lesions, despite the presence of vertical growth-like patterns, are difficult to assess. In defense of the concept, the occasional documentation of a metastasizing example can be cited.
That occasional Spitz nevus-like lesions metastasize is accepted; the features which set the occasional metastasizing example apart from a much larger store of non-metastasizing lesions have not be reliably defined.
A reliance on vertical growth-like patterns is basic to a definition of minimal deviation variant melanomas. The task is easier for examples in which the patterns of vertical
growth are typical than for those in which the patterns are variant or migrant ( WHITHERS1, 2, & 3); in
other words, a compact nodule is a more reliable correlate of melanoma than a vertical growth-like pattern in which nests and fascicles are loosely spaced in a widened papillary dermis (variant VG-like patterns), or
in which nests and fascicles, or even individual cells, infiltrate the reticular dermis among preexisting collagen bundles (migrant VG-like patterns). A variant vertical growth-like pattern is basic to the diagnosis
of the common combined nevus. In most other aspects, the common combined nevus would satisfy criteria for the diagnosis of minimal deviation melanoma. There are rare examples of combined nevus-like lesions in which
nests of atypical cells are closely aggregated in typical vertical growth-like patterns; some of these exceptions also have been associated with regional nodal metastases; there is a lesion with combined nevus-like
qualities which occasionally is associated with metastases (i.e., MDM of combined nevus-like type).
Much of what currently is classified as melanoma is an artifice, as a manifestation of a taxonomic compromise; a large number of such cases are examples of evolving neoplasia in which some of the histologic
features of true, biologically life-threatening melanomas are manifested. The one exceptional quality of many of these borderline neoplasms is size, particularly vertical dimensions. Breslow’s criteria are validated
as an indicator of a significant risk for metastasis only beyond a certain boundary (i.e., 1.5 mm in vertical dimensions). The concept of minimal deviation melanoma implies that there are alternate pathways along
which a neoplasm evolves to the state of a metastasizing malignancy. In addition, the patterns of the common melanomas display a more predictable correlation with a capacity for metastasis than is manifested in the
variant categories; the relationships are size-related for the common melanomas; the relationships which validate Breslow’s criteria are size-dependent. For common melanomas, the dependence on size as a validator of
Breslow’s criteria suggests that below certain limits the behavior of common melanomas will prove to be erratic and unpredictable; more lesions below a certain limit in size will be “benign” than “malignant,”
regardless of the selected terminology. The small, taxonomic “common melanomas” (thin lesion in vertical growth but measuring less than 1mm in vertical dimensions) are so early along their evolutional pathways that
they too can be accommodated in the concept of Minimal Deviation Melanoma.
With this brief background, the patterns in the Consultation Case can be compared with the virtual images of variant nevi.
One approach to an understanding of the patterns in the problem lesion might be a characterization of any associated precursor (i.e., dysplasia). Here, we would evaluate the patterns represented in the Pictorial1 Page. Some of the patterns are lentiginous and junctional and the degree of atypia is moderate. In contrast to the features of markers for the dysplastic nevus syndrome, the lentiginous and junctional components of the consultation case are not associated with significant markers for host immune response (i.e., lymphoid infiltrates and lamellar fibrosis of the papillary dermis). Some of the dysplastic lesions in the setting of multiple halo nevi are pure cytologic dysplasias without lymphoid infiltrates. If these are lesions of the same basic order as the classic halo nevi, then they may represent a stage in the neoplastic phenomena leading to dysplastic (atypical) halo nevi, but they lack inflammation because they have not attained the requisite stage of genetic transformation. Perhaps in this category, some of the lesions display the cytologic features of dysplasia but lack the phenotype which elicits the lymphoid infiltrates. They might be an initial manifestation; the halo nevus response may be associated with a more advanced neoplastic transformation. Even in classic halo nevi, the evidence of cytologic atypia may be confined to a dermal population of “nevus” cells in the absence of a lentiginous and junctional component. Such lesions might be characterized as dermal dysplasias of halo nevus type. The consultation case has markers for both lentiginous and junctional (P1-1&4), and dermal dysplasia (P1-7 & 8). A prominent component of lymphoid cells is not a feature of any portion of the lesion. The lymphoid infiltrates are few in number and focal in distribution
(P1- 8). If we evaluate patterns in the vertical growth-like component (P2-1, 2, 4, 6, & 7), the spindle cell quality of
the neoplastic cells might be offered in support of a halo nevus-like quality.
The lentiginous and junctional components of halo nevi frequently are expressed in spindle cell patterns. The patterns in the consultation case would offer support for a characterization of the lesion as showing a
“primary configuration;” the patterns would suggest that the dermal population of cells in the vertical growth-like component are progeny of the population of cells in lentiginous and junctional component (P2-2). Minimal deviation melanomas of halo nevus-like type (see INDEX3) which evolve in a primary configuration are usually characterized by a reduction in the density of lymphoid infiltrates in the dermal vertical growth component that is newly
arrived from the epidermal component, when comparisons are made with remnant of the precursor halo nevus. Although, a peculiar minimal deviation melanoma of halo nevus-like type (ab inflammation) cannot be excluded,
it would be difficult to defend such a fanciful assignment.
If we reduce the virtual images of a classic Spitz nevus to words and then use the virtual images embodied in these words for an evaluation of the real images of this problem case,
we will find many corollaries. The patterns of the problem case are characterized by spindle cells in fascicles and by loose spacing of the fascicles in the dermis; these are positive correlations. We will have
satisfied the need to identify spindle cells and will have additionally identified epithelioid qualities. If we then translate the designation of Spitz nevus into that of a “spindle and epithelioid cell” nevus , we
will have gone a long way in making a diagnosis of Spitz nevus (the ease with which one can supplant the other is obvious). On the other hand, if we rely on stored virtual images rather than those embodied in words,
the patterns and cytologic features deviate from those of classic Spitz nevus. At every opportunity, an observer should reinforce his stores of images for making the diagnosis of classic Spitz nevus and should in
turn be cautious in assigning the designation to lesions which show deviant patterns and cytologic features. Qualifications are required. Particular caution is required for those cases in which the deviations are
focally associated with more classic patterns of Spitz nevus (a marker for an earlier stage in the evolution of a progressive neoplasm) or even with a remnant of an “atypical” Spitz nevus-like lesion, as in
the problem case. The loose spacing of fascicles in the upper portion of the lesion might also be cited as a Spitz nevus-like quality. On the other hand, this spacing of cells also satisfies the requisites for the
recognition of either variant (fascicles loosely spaced but confined to a widened papillary dermis) or migrant (fascicles insinuating among collagen bundles of the reticular dermis) vertical growth.
Although there are components of the problem case which might be characterized as representing the emergence of a dysplastic population in the background of a common nevus, the
patterns deviate from those usually associated with the common premalignant melanocytic dysplasia-melanoma sequence. The lesion clearly is not an example of common superficial spreading melanoma. Depending on
personal whims, some observers might emphasize halo nevus-like qualities and others might favor a Spitz nevus-like variant.
The lesion illustrated in PICTORIAL3 is a study in ambiguities. It is of a type which does not lend itself to pattern analysis, as the sole technique of the microscopist. There is a hint on one of the section of halo nevus-like phenomena. Once this parcel is opened, then many of the other features, including the fascicular patterns, the spindle cell cytology, the lateral spread in lentiginous and junctional patterns, and the lymphoid infiltrates find a home. The limited nature of the infiltrates is something of a stumbling block. It may be that nature has exposed one of her secrets to be shared, if only we are able to get beyond pattern analysis. One of us has proposed that in halo nevus there is a primary genetic alteration of the affected melanocytic cells and that the characteristic host immune response is a flag that the neoplasm has entered a pathway to progressive neoplasia, but one other than the common pathways. In the lesion in P3-1-5, we may have been treated to the cytologic features of this genetic alteration and of the alternate pathway without the masquerade of a distinctive
pattern of host immune response.
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