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Minimal deviation melanoma (MDM) is a characterization for stages of melanocytic neoplasia that are not fully accommodated in the standard
definitions of the common melanomas. In this approach, a melanoma is a melanocytic lesion in vertical growth (see: WHITHERS in MASTER BORDER to left). The progressions of melanocytic neoplasia prior to the emergence of vertical growth (i.e., as a precursor to melanoma in vertical growth) qualify as dysplasia or atypical nevus. Classic superficial spreading melanoma (SSM) has been excluded from the minimal deviation category; in this approach, large cell melanomas in either spindle cell or round cell patterns in vertical growth and with a radial growth component are acceptable as variants of SSM (with reservation regarding site and with requisites regarding histologic features). Nodular melanomas showing a comparable degree of cytologic atypia in large cell patterns also have been generally excluded from the domain of MDM. On the other hand, some stages in the neoplastic progressions leading to classic forms of SSM (i.e., early stages leading from precursor to melanoma) and some examples of ‘nodular melanoma’) can be accommodated in the definition. A melanocytic neoplasm in vertical growth (i.e., a lesion satisfying the requisites for the diagnosis of melanoma) showing the pattern of the common final pathway in its epidermal component but lesser degrees of atypia in a vertical growth component which measures less than 1.0 mm in vertical dimensions can be accommodated in the category of minimal deviation melanoma. It also can be characterized as borderline or intermediate melanocytic neoplasia of indeterminate malignant potential; distinctions between the two categories (i.e., common melanomas and MDM) can be defined by vertical dimensions of the vertical growth component. For variants of lentigo maligna melanoma, the leeway for inclusion in the category of MDM is great with the caveat that a decision to classify a lesion in the minimal deviation category depends on the degree of atypia in the vertical growth component rather than the cytologic features of the epidermal component. By definition, lentigo maligna melanoma is to be distinguished from SSM; in its setting (i.e., sun-exposed skin), a melanocytic neoplasm may enter vertical growth prior to the appearance of those clones whose cytologic and histologic characteristics define SSM (i.e., the ‘large cell’ patterns of the common final pathway: see WHITHERS). Melanocytic neoplasms, that enter vertical growth prior to the emergence of the patterns of the common final pathway, generally are prominently lentiginous.
Similarly, examples of acral lentiginous melanoma may be characterized as minimal deviation variants, if the degree of atypia in the vertical growth component is moderate to moderately severe (i.e., something less
than large cell features) and if the vertical dimensions are less than 1.0 mm (the degree of dysplasia of the epidermal component is not the determinate in this approach).
Having granted all these exceptions and having validated the common variants as defined above, there remains a group of melanocytic neoplasms in which patterns of
vertical growth are nevoid. These patterns are associated with either the cytologic features and/or the patterns of host immune response which provide a basis for comparing the overall patterns to those of variant
nevi. In this approach, it is possible to define atypical variant nevi whose cytologic features differ from those of common nevi. Such lesions often are associated with markers for host immune response. For such
lesions to qualify as atypical nevi, fully developed vertical growth patterns should not be represented. If a vertical growth component is represented, then the lesion (as defined above) qualifies as a MDM, and
attempts should be made to subtype the variant. For MDM whose vertical growth component measures less than 1.5 mm in vertical dimensions, the lesion can be qualified as borderline (less than 1 mm in vertical
dimensions) or intermediate (1 to 1.5 mm in vertical dimensions) in type (the lesions become ‘qualified’ MDM). Depending on the care in searching out variant nevus-like features, the following variants of atypical
nevi and respective minimal deviation melanomas may be defined: 1.) halo nevus-like, 2.) Spitz nevus-like, 3.) pigmented spindle cell nevus-like, 4.) acquired or congenital nevus-like, 5.) and combined nevus-like.
The structuring of a category of MDM requires a molding of new virtual images; preconceived notions of which parcels of virtual images are required for the
definition of the respective models of the variant nevi must be restructured with new sets of virtual images. If confronted with a problematic lesion, we often find ourselves attempting to accommodate an
unusual neoplasm in the parcel of virtual images of use in defining variant nevi. Thus an atypical spindle cell neoplasm of unusual type might be compared to a Spitz nevus; in turn, it might then, with the
parcels that have been promoted as having utility for the interpretation of a Spitz nevus, be interpreted as a Spitz nevus; in this approach, arbitrariness is required. We might alternately consider the
precursors of minimal deviation melanomas to be atypical melanocytomas of either spindle or round cell types. We might then think of this group of lesions as new neoplasias rather than modified variant nevi; they
may resemble variant nevi and the resemblances should be recorded in the descriptions and the diagnosis. The variations may well have biologic import.
The material on this site is a presentation of a nevoid, minimal deviation melanoma with halo nevus-like features. The lesion was removed by a biopsy in 1994.
With a diagnosis of minimal deviation melanoma, the area was re-excised and margins were clearly free of involvement. Recently, the patient returned with an enlarged regional node which was excised. The excised node
measured approximately 1.5 cm. in diameter.
DIRECTORY
This site is structured in 3 tiers. The first tier is the home site and consists of one (this) chapter. The second tier will be a presentation in two chapters.
The first chapter will be a presentation of findings and the second chapter will be a discussion. The third tier will include four chapters, each of which will include a series of pictorials.
Navigation guides are included in the margin to the left. With these guides it should be possible to maneuver back and forth from chapter to chapter and even to
external sites. In searching for navigation guides do not be misled, if you seem to have arrived at the end of text (and of the chapter) without finding the appropriate guide; just follow the margin on the left to
its end (which often is beyond the end of the text). In the margin at some level, there should be a guide to lead you to the chapter of your choice. At the end of each layout of each chapter at all the tiers,
there is a navigation bar giving access to both Tier 1 and Tier 2. At Tier 2 in Chapter2, navigation bars in the left margin will be found to take the reader to each of the pictorials at Tier 3. At Home (i.e., this
chapter), the following indices will take you to individual chapters and also to individual photomicrographs.
CHAPTER INDEX
Chapter 1 (Home): instructions and indices
Chapter 2 (Introduction): a presentation of basic concepts related to the interpretation of halo nevus-like
variants and an integration of these concepts and histologic patterns
Chapter 3 (Conclusion): the relativity of halo nevus-like phenomena and melanocytic neoplastic
progressions: anticipation of criticisms
Chapter 4 (Pictorial 1): a presentation of basic patterns as seen at low magnification
Chapter 5 (Pictorial 2): a presentation of halo nevus-like phenomena and the
implications of the histologic features
Chapter 6 (Pictorial 3): a presentation of vertical growth-like patterns with emphasis of the variant type
Chapter 7 (Pictorial 4): a presentation of the histologic features with comments on
disparities between the patterns in the primary lesion and in the metastasis.
IMAGE INDEX
The prefix ‘C’ followed by a number identifies the chapter (numbered in sequence primarily from tier to tier and then secondarily at the level of each tier. The
prefix ‘P’ followed by a number identifies the pictorials in sequence at tier 3. There are four pictorials each containing a variable number of photomicrographs at this tier. P1 is Chapter 4 at tier 3.
C4P1-1: overall pattern with definition of interface between vertical growth and
nevus-like remnant : C4P1-2 & C4P1-3: progressive levels of
magnification show the same basic patterns and the relativity of size to the appropriatenes of an unqualified diagnosis of melanoma: introduction of focal regression : C4P1-4: variant vertical growth-like patterns and their significance: C4P1-5:
variant vertical growth-like pattern contrasted with nevus-like component:
C5P2-1 & C5P2-2: lymphoid infiltrates of halo nevus-like phenomena and significance of epithelioid cells : C5P2-3: halo nevus-like phenomena and cytolysis: epithelioid cells: C5P2-4 & C5P2-5: cytolytic defects and
epithelioid cells :
C6P3-1, C6P3-2, & C6P3-3: variant vertical growth in primary configuration: C6P3-4: radial growth:
C7P4-1: overall pattern of metastasis to a lymph node: C7P4-2; solid patterns and large cell characteristics : C7P4-3:
area of degeneration with melanogenic cell: focal neuroid qualities : C7P4-4: HMB45 positivity: C7P4-5: S-100 protein positivity:
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